Fluorinated unsaturated cyclic carbonate and process for producing the same

ABSTRACT

An electrolyte solution containing a compound represented by the following formula (1): 
                         
wherein Rf is a C1-C8 fluorinated alkyl group, and vinylene carbonate. Also disclosed is an electrochemical device including the electrolyte solution, a lithium ion secondary battery including the electrolyte solution and a module including the lithium ion secondary battery.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Rule 53(b) Continuation Application of application Ser. No.15/528,017 filed May 18, 2017, which is a National Stage ofInternational Application No. PCT/JP2015/082542, filed Nov. 19, 2015,which claims priority from Japanese Patent Application No. 2014-236700filed Nov. 21, 2014, the contents of all of which are incorporatedherein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a novel fluorinated unsaturated cycliccarbonate and a process for producing the same.

BACKGROUND ART

Patent Literature 1 discloses a vinylene carbonate represented by thefollowing formula (1).

In the formula (1), R¹ and R² may be the same as or different from eachother, and are each a hydrogen atom, a halogen atom, or a C1-C12 alkylgroup which may optionally contain a halogen atom.

Patent Literature 2 discloses the following formula.

Patent Literature 3 discloses a compound represented by the following(Formula 4):

wherein R₉ and R₁₀ are each hydrogen, fluorine, chlorine, a C1-C3 alkylgroup, or a fluorinated alkyl group, and R₉ and R₁₀ may be the same asor different from each other.

Patent Literature documents 4 to 7 also disclose unsaturated cycliccarbonates.

Although each of these documents specifically discloses the use of anelectrolyte solution containing vinylene carbonate or a fluorinatedcarbonate, they disclose neither actual use of an unsaturated cycliccarbonate containing a fluorinated alkyl group nor any method forsynthesizing or acquiring the same.

CITATION LIST Patent Literature

Patent Literature 1: JP 2003-257479 A

Patent Literature 2: JP 2007-317647 A

Patent Literature 3: JP 2006-164860 A

Patent Literature 4: JP 2006-294414 A

Patent Literature 5: JP 2011-100750 A

Patent Literature 6: JP 2006-286570 A

Patent Literature 7: JP 2006-179458 A

SUMMARY OF INVENTION Technical Problem

As mentioned above, an unsaturated cyclic carbonate containing afluorinated alkyl group and the usefulness thereof have never been knownbefore the filing date of this application.

In consideration of the above state of the art, the present inventionaims to provide an unsaturated cyclic carbonate containing a fluorinatedalkyl group and a process for producing the same.

Solution to Problem

The present invention relates to a compound represented by the followingformula (1):

wherein Rf is a C1-C8 fluorinated alkyl group.

In the formula (1), Rf is preferably a C2-C8 fluorinated alkyl group.

The present invention also relates to an electrolyte solution containingthe above compound.

The present invention also relates to an electrochemical devicecontaining the above electrolyte solution.

The present invention also relates to a lithium ion secondary batterycontaining the above electrolyte solution.

The present invention also relates to a module including the abovelithium ion secondary battery.

The present invention also relates to a production process including

reacting a compound (2-1) represented by the following formula (2-1):

wherein X is a halogen atom, with a fluoroalkylating agent to provide acompound represented by the following formula (1):

wherein Rf is a C1-C8 fluorinated alkyl group.

The present invention also relates to a production process including

reacting a compound (3-1) represented by the following formula (3-1):

wherein Rf is a C1-C8 fluorinated alkyl group, with a halogenating agentto provide a compound (3-2) represented by the following formula (3-2):

wherein Rf is defined in the same manner as mentioned above; and X is ahalogen atom, andreacting the compound (3-2) with a base or metal to provide a compoundrepresented by the following formula (1):

wherein Rf is defined in the same manner as mentioned above.

The present invention also relates to a production process including

reacting a compound (4-1) represented by the following formula (4-1):

wherein Rf is a C1-C8 fluorinated alkyl group, with carbon dioxide toprovide a compound (4-2) represented by the following formula (4-2):

wherein Rf is defined in the same manner as mentioned above, andreacting the compound (4-2) with a base or metal to provide a compoundrepresented by the following formula (1):

wherein Rf is defined in the same manner as mentioned above.

The present invention also relates to a production process includingreacting vinylene carbonate with a compound (5-1) represented by thefollowing formula (5-1):Rf—Xwherein Rf is a C1-C8 fluorinated alkyl group; and X is a halogen atom,to provide a compound (5-2) represented by the following formula (5-2):

wherein Rf is defined in the same manner as mentioned above; and X is ahalogen atom, andreacting the compound (5-2) with a base or metal to provide a compoundrepresented by the following formula (1):

wherein Rf is defined in the same manner as mentioned above.

Advantageous Effects of Invention

The present invention can provide an unsaturated cyclic carbonatecontaining a fluorinated alkyl group. This novel unsaturated cycliccarbonate is useful as a component constituting an electrolyte solutionto be used in an electrochemical device such as a lithium ion secondarybattery.

DESCRIPTION OF EMBODIMENTS

The present invention will be specifically described hereinbelow.

The novel compound of the present invention is a fluorinated unsaturatedcyclic carbonate represented by the following formula (1):

wherein Rf is a C1-C8 fluorinated alkyl group.

In the formula (1), Rf may be either a perfluorinated alkyl group or apartially fluorinated alkyl group, and is preferably a perfluorinatedalkyl group. Rf may contain an ether bond.

In the formula (1), the fluorinated alkyl group may be either linear orbranched.

In the formula (1), Rf has a carbon number of 8 or less, preferably 6 orless. Rf may have a carbon number of 2 or more.

In the formula (1), Rf is preferably at least one selected from thegroup consisting of CF₃—, CF₃CF₂—, CF₃CF₂CF₂—, CF₃CF₂CF₂CF₂—,CF₃CF₂CF₂CF₂CF₂—, CF₃CF₂CF₂CF₂CF₂CF₂—, CF₃CF₂CF₂CF₂CF₂CF₂CF₂—,CF₃CF₂CF₂CF₂CF₂CF₂CF₂CF₂—, (CF₃)₂CF—, CF₃CH₂—, CF₃CF₂CH₂—,CF₃CF₂CF₂CH₂—, CF₃CF₂CF₂CF₂CH₂—, CF₃CF₂CF₂CF₂CF₂CH₂—,CF₃CF₂CF₂CF₂CF₂CF₂CH₂—, CF₃CF₂CF₂CF₂CF₂CF₂CF₂CH₂—,CF₃CF₂CF₂CF₂CF₂CF₂CF₂CF₂CH₂—, and (CF₃)₂CFCH₂—, more preferably at leastone selected from the group consisting of CF₃—, CF₃CF₂—, CF₃CF₂CF₂—,CF₃CF₂CF₂CF₂—, CF₃CF₂CF₂CF₂CF₂CF₂—, and (CF₃)₂CF—.

The above novel compound can suitably be produced by any of thefollowing four methods.

A first production process includes reacting a compound (2-1)represented by the following formula (2-1):

(wherein X is a halogen atom) with a fluoroalkylating agent to provide acompound represented by the following formula (1):

(wherein Rf is a C1-C8 fluorinated alkyl group).

In other words, the first production process provides the targetfluorinated unsaturated cyclic carbonate by fluoroalkylation of a knownhalogenated unsaturated cyclic carbonate.

X in the formula (2-1) is a halogen atom, and is preferably a fluorineatom, a chlorine atom, a bromine atom, or an iodine atom, morepreferably a chlorine atom, a bromine atom, or an iodine atom,particularly preferably a bromine atom or an iodine atom.

The first production process is classified into three processes, i.e.,Process (1-1) of using a telomer as a fluoroalkylating agent, Process(1-2) of using a mercury compound as a fluoroalkylating agent, andProcess (1-3) of using a silicon compound as a fluoroalkylating agent.

In Process (1-1), preferred examples of a compound to be used as thefluoroalkylating agent include compounds represented by RfI (Rf is aC1-C8 fluorinated alkyl group) and compounds represented by RfBr (Rf isdefined in the same manner as mentioned above). More preferred examplesthereof include perfluoroalkyl iodides and perfluoroalkyl bromides.

In Process (1-1), the reaction between the compound (2-1) and thefluoroalkylating agent is preferably performed in an organic solvent.Preferred examples of the organic solvent include diethyl ether,diisopropyl ether, ethyl methyl ether, cyclopentyl methyl ether,methyl-t-butyl ether, and tetrahydrofuran. More preferred examplesthereof include cyclopentyl methyl ether, methyl-t-butyl ether, andtetrahydrofuran. Particularly preferred are cyclopentyl methyl ether andtetrahydrofuran.

In Process (1-1), the reaction between the compound (2-1) and thefluoroalkylating agent is preferably performed in the presence of zincand a transition metal catalyst. Preferred examples of the transitionmetal catalyst include palladium chloride, palladium acetate,bistriphenylphosphinepalladium dichloride, bis(p-cyanophenyl)palladiumdichloride, tetrakistriphenylphosphinepalladium,bisacetylacetonatopalladium, and bisdibenzylideneacetonepalladium. Morepreferred are palladium acetate, bistriphenylphosphinepalladiumdichloride, and tetrakistriphenylphosphinepalladium.

In Process (1-1), the reaction between the compound (2-1) and thefluoroalkylating agent may be performed under ultrasonic irradiation.

In Process (1-1), the reaction can be quenched by adding an aqueoussolution such as an aqueous solution of sodium chloride. Addition of theaqueous solution to the reaction solution causes separation of thesolution into two layers. A solution containing the compound (1) can bethen obtained by collecting an organic layer by liquid separation.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the resultingsolution containing the compound (1), to filter out the desiccant andcollect the solution containing the compound (1) as a filtrate, and thento concentrate the solution.

The compound (1) can be highly purified by distilling the resultingsolution containing the compound (1) or sublimating the compound (1)from the solution. The purification technique is not limited todistillation or sublimation. If desired, the purification can beachieved by any known purification technique such as solvent extraction,drying, filtering, distillation, concentration, column chromatography,recrystallization, and any combination thereof.

In Process (1-2), preferred examples of a compound to be used as thefluoroalkylating agent include compounds represented by Rf₂Hg (Rf is aC1-C8 fluorinated alkyl group). More preferred examples thereof include(CF₃)₂Hg, (C₂F₅)₂Hg, and (C₆F₁₃)₂Hg.

In Process (1-2), the reaction between the compound (2-1) and thefluoroalkylating agent is preferably performed in an organic solvent.Preferred examples of the organic solvent include N-methylpyrrolidone,dimethylformamide, dimethylacetamide, acetone, methyl acetate, ethylacetate, diethyl ether, diisopropyl ether, tetrahydrofuran, glyme,tetraglyme, and sulfolane. More preferred examples thereof includeN-methylpyrrolidone, dimethylformamide, dimethylacetamide, acetone,methyl acetate, ethyl acetate, diethyl ether, glyme, tetraglyme, andsulfolane. Particularly preferred are N-methylpyrrolidone,dimethylformamide, dimethylacetamide, and sulfolane.

In Process (1-2), the reaction between the compound (2-1) and thefluoroalkylating agent is preferably performed in the presence of asimple metal or a metal salt. Preferred examples of the simple metalinclude zinc and copper. More preferred is copper. Preferred examples ofthe metal salt include copper fluoride, copper chloride, copper bromide,and copper iodide. More preferred are copper bromide and copper iodide.The reaction can be performed in the presence of both a simple metal anda metal salt.

In Process (1-2), the reaction can be quenched by adding an aqueoussolution such as an aqueous solution of sodium chloride. Addition of theaqueous solution to the reaction solution causes separation of thesolution into two layers. A solution containing the compound (1) can bethen obtained by collecting an organic layer by liquid separation.

In Process (1-2), a water-insoluble organic solvent may be added to thereaction solution before the liquid separation so as to improve theliquid-separating performance. Examples of the water-insoluble organicsolvent include diethyl ether, diisopropyl ether, and ethyl acetate.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the resultingsolution containing the compound (1), to filter out the desiccant andcollect the solution containing the compound (1) as a filtrate, and thento concentrate the solution.

The compound (1) can be highly purified by distilling the resultingsolution containing the compound (1) or sublimating the compound (1)from the solution. The purification technique is not limited todistillation or sublimation. If desired, the purification can beachieved by any known purification technique such as solvent extraction,drying, filtering, distillation, concentration, column chromatography,recrystallization, and any combination thereof.

In Process (1-3), preferred examples of a compound to be used as thefluoroalkylating agent include compounds represented by RfTMS (Rf is aC1-C8 fluorinated alkyl group; and TMS is a trimethylsilyl group) andcompounds represented by RITES (Rf is defined in the same manner asmentioned above; and TES is a triethylsilyl group). More preferredexamples thereof include CF₃TMS, C₂F₅TMS, C₄F₉TMS, C₆F₁₃TMS, CF₃TES,C₂F₅TES, C₄F₉TES, and C₆F₁₃TES.

In Process (1-3), the reaction between the compound (2-1) and thefluoroalkylating agent is preferably performed in an organic solvent.Preferred examples of the organic solvent include N-methylpyrrolidone,dimethylformamide, dimethylacetamide, dimethylpropyleneurea, glyme,tetraglyme, and sulfolane. More preferred examples thereof includeN-methylpyrrolidone, dimethylformamide, dimethylacetamide, anddimethylpropyleneurea. Particularly preferred are N-methylpyrrolidone,dimethylformamide, and dimethylpropyleneurea.

In Process (1-3), the reaction between the compound (2-1) and thefluoroalkylating agent is preferably performed in the presence of acopper salt and a metal fluoride. Preferred examples of the copper saltinclude copper fluoride, copper chloride, copper bromide, copper iodide,and copper acetate. More preferred are copper chloride and copperiodide. Preferred examples of the metal fluoride include lithiumfluoride, sodium fluoride, and potassium fluoride. More preferred ispotassium fluoride.

In Process (1-3), the reaction between the compound (2-1) and thefluoroalkylating agent may be performed in the presence of a ligand.Preferred examples of the ligand include 1,10-phenanthroline,tetramethylethylenediamine, and 2,2′-bipyridine. Particularly preferredare 1,10-phenanthroline and 2,2′-bipyridine.

In Process (1-3), the reaction can be quenched by adding an aqueoussolution such as an aqueous solution of sodium chloride. Addition of theaqueous solution to the reaction solution causes separation of thesolution into two layers. A solution containing the compound (1) can bethen obtained by collecting an organic layer by liquid separation.

In Process (1-3), a water-insoluble organic solvent may be added to thereaction solution before the liquid separation so as to improve theliquid-separating performance. Examples of the water-insoluble organicsolvent include diethyl ether, diisopropyl ether, and ethyl acetate.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the resultingsolution containing the compound (1), to filter out the desiccant andcollect the solution containing the compound (1) as a filtrate, and thento concentrate the solution.

The compound (1) can be highly purified by distilling the resultingsolution containing the compound (1) or sublimating the compound (1)from the solution. The purification technique is not limited todistillation or sublimation. If desired, the purification can beachieved by any known purification technique such as solvent extraction,drying, filtering, distillation, concentration, column chromatography,recrystallization, and any combination thereof.

A second production process includes reacting a compound (3-1)represented by the following formula (3-1):

(wherein Rf is a C1-C8 fluorinated alkyl group) with a halogenatingagent to provide a compound (3-2) represented by the following formula(3-2):

(wherein Rf is defined in the same manner as mentioned above; and X is ahalogen atom), and reacting the compound (3-2) with a base to provide acompound represented by the following formula (1):

(wherein Rf is defined in the same manner as mentioned above).

In other words, the second production process provides the targetfluorinated unsaturated cyclic carbonate by halogenation of a knownfluorinated saturated cyclic carbonate and the followingdehydrohalogenation of the resulting compound. The fluorinated saturatedcyclic carbonate obtained by the halogenation needs not to be isolated,and can be subjected to the dehydrohalogenation as it is.

Rf in each of the formula (3-1) and the formula (3-2) is defined in thesame manner as Rf in the aforementioned formula (1).

X in the formula (3-2) is a halogen atom, and is preferably a chlorineatom, a bromine atom, or an iodine atom.

The halogenating agent to be used may be a single halogen such asfluorine (F₂), chlorine (Cl₂), bromine (Br₂), or iodine (I₂), or ahalogenating reagent. Preferred among these is fluorine (F₂), chlorine(Cl₂), bromine (Br₂), or a halogenating reagent.

The reaction between the compound (3-1) and the simple halogen can beperformed in a solvent, preferably in an organic solvent such as ahalogen-containing solvent. If fluorine is used as a halogen, theorganic solvent is preferably a fluorine-containing solvent. Ifchlorine, bromine, or iodine is used, the reaction is preferablyperformed in carbon tetrachloride or a like organic solvent.

Also in the case of using a halogenating reagent, the above reaction canbe performed in an organic solvent. The organic solvent in this case maybe any organic solvent that does not react with a base to be used in thenext step.

The halogenating reagent may be any of those containing a fluorine atom(fluorinating agents), those containing a chlorine atom (chlorinatingagents), those containing a bromine atom (brominating agents), and thosecontaining an iodine atom (iodizing agents).

Examples of the fluorinating agents include 1-fluoropyridiniumtetrafluoroborate, 1-fluoropyridinium triflate,1-fluoro-2,4,6-trimethylpyridinium tetrafluoroborate,1-fluoro-2,4,6-trifluoromethylpyridinium trifluoromethanesulfonate,N-fluoro-N′-(chloromethyl)-triethylenediaminebis(tetrafluoroborate),N-fluorobenzenesulfonimide, tetrabutylammonium difluorotriphenyltin,2,6-dichloro-1-fluoropyridinium trifluoromethanesulfonate, and1,1′-difluoro-2,2′-bipyridinium bis(tetrafluoroborate). Preferred isN-fluoro-N′-(chloromethyl)-triethylenediaminebis(tetrafluoroborate) orN-fluorobenzenesulfonimide.

Examples of the chlorinating agents include tert-butyl hypochlorite,N-chlorophthalimide, N-chlorosuccinimide, cyanuric chloride, oxalylchloride, sodium dichloroisocyanurate, trichloroisocyanuric acid,trichloromethane, and thionyl chloride. Preferred isN-chlorophthalimide, N-chlorosuccinimide, oxalyl chloride,trichloromethane, or thionyl chloride.

Examples of the brominating agents include boron tribromide,N-bromoacetamide, bromodimethyl bromide, N-bromophthalimide,N-bromosaccharin, N-bromosuccinimide, 1-butyl-3-methylimidazoliumtribromide, 1,3-dibromo-5,5-dimethylhydantoin, dibromoisocyanuric acid,5,5-dibromomeldrum's acid, 4-dimethylaminopyridinium bromide perbromide,pyridinium bromide perbromide, 2,4,4,6-tetrabromo-2,5-cyclohexadienone,tetrabutylammonium tribromide, trimethylphenylammonium bromide, andtriphenylphosphine dibromide. Preferred is boron tribromide,N-bromophthalimide, N-bromosuccinimide,1,3-dibromo-5,5-dimethylhydantoin, dibromoisocyanuric acid, or5,5-dibromomeldrum's acid.

Examples of the iodizing agents include1,3-diiodo-5,5-dimethylhydantoin, N-iodosaccharin, andN-iodosuccinimide.

The reaction between the compound (3-1) and the simple halogen can beprogressed by applying heat or light. The light is preferablyultraviolet rays.

Then, the reaction can be quenched by adding a reducing agent. Thereducing agent may be added in the form of an aqueous solution. When thereaction between the compound (3-1) and the halogenating agent isperformed in a water-insoluble organic solvent, addition of the reducingagent in the form of an aqueous solution to the reaction product causesseparation of the solution into two layers. A solution containing thecompound (3-2) can be then obtained by collecting an organic layer byliquid separation.

Next, the compound (3-2) is reacted with a base or metal.

This reaction can be performed in the solvent used in the reaction forproviding the compound (3-2). Alternatively, it is acceptable to distillthe solvent from the solution containing the compound (3-2) and to add asolvent that is different from the solvent used in the reaction forproviding the compound (3-2), and then to react the compound (3-2) witha base or metal in this solvent.

The base may be either an organic base or an inorganic base. Preferredamong these are triethylamine, diisopropylethylamine, andtert-butoxypotassium.

The metal is preferably zinc.

The base or metal may be added to the solution containing the compound(3-2) which is collected after the reaction is quenched by adding thereducing agent. Alternatively, the reducing agent and the base or metalmay be added at the same time to a solution obtained by reacting thecompound (3-1) and the halogenating agent. In this case, the two stepscan be successively performed in the same container.

Then, the reaction can be quenched by adding an acidic aqueous solution.When the reaction between the compound (3-2) and the base or metal isperformed in a water-insoluble organic solvent, addition of the acidicaqueous solution to the reaction product causes separation of thesolution into two layers. A solution containing the compound (1) can bethen obtained by collecting an organic layer by liquid separation.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the resultingsolution containing the compound (1), to filter out the desiccant andcollect the solution containing the compound (1) as a filtrate, and thento concentrate the solution.

The compound (1) can be highly purified by distilling the resultingsolution containing the compound (1) or sublimating the compound (1)from the solution. The purification technique is not limited todistillation or sublimation. If desired, the purification can beachieved by any known purification technique such as solvent extraction,drying, filtering, distillation, concentration, column chromatography,recrystallization, and any combination thereof.

A third production process includes reacting a compound (4-1)represented by the following formula (4-1):

(wherein Rf is a C1-C8 fluorinated alkyl group) with carbon dioxide toprovide a compound (4-2) represented by the following formula (4-2):

(wherein Rf is defined in the same manner as mentioned above), andreacting the compound (4-2) with a base to provide a compoundrepresented by the following formula (1):

(wherein Rf is defined in the same manner as mentioned above).

In other words, the third production process provides the targetfluorinated unsaturated cyclic carbonate by allowing carbon dioxide toact on a known fluorinated epoxy compound to provide a fluorinatedsaturated cyclic carbonate and the following dehydrohalogenation of theresulting fluorinated saturated cyclic carbonate. The fluorinatedsaturated cyclic carbonate obtained needs not to be isolated, and can bedirectly subjected to the dehydrohalogenation.

Rf in each of the formula (4-1) and the formula (4-2) is defined in thesame manner as Rf in the aforementioned formula (1).

The reaction between the compound (4-1) and carbon dioxide can beperformed in a solvent, and the solvent may be either an organic solventor water. Preferred examples of the organic solvent includeN-methylpyrrolidone, dimethylformamide, acetone, methyl acetate, ethylacetate, diethyl ether, diisopropyl ether, tetrahydrofuran, glyme,tetraglyme, and sulfolane. More preferred examples thereof includeN-methylpyrrolidone, dimethylformamide, acetone, methyl acetate, ethylacetate, diethyl ether, glyme, tetraglyme, and sulfolane. Particularlypreferred are N-methylpyrrolidone, dimethylformamide, acetone, andsulfolane.

The reaction between the compound (4-1) and carbon dioxide is preferablyperformed in the presence of a salt. The salt is preferably at least oneselected from the group consisting of NaF, NaCl, NaBr, NaI, LiF, LiCl,LiBr, LiI, KF, KCl, KBr, and KI, more preferably at least one selectedfrom the group consisting of LiF, LiCl, LiBr, and LiI.

The reaction between the compound (4-1) and carbon dioxide can beperformed at 0° C. to 100° C., preferably 15° C. to 80° C.

In the case of using an organic solvent in the reaction, the reactioncan be quenched by adding, for example, water.

In the case of using water as a solvent in the reaction, the quenchingmay be replaced by extraction using an organic solvent.

When the reaction between the compound (4-1) and carbon dioxide isperformed in a water-soluble organic solvent and the reaction isquenched by adding water, addition of a water-insoluble organic solventto the reaction product causes separation of the solution into twolayers. A solution containing the compound (4-2) can be then obtained bycollecting an organic layer by liquid separation. Examples of thewater-insoluble organic solvent include diethyl ether, diisopropylether, and ethyl acetate.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the solutioncontaining the compound (4-2), and to filter out the desiccant andcollect the solution containing the compound (4-2) as a filtrate. Thissolution may be subjected to the next step.

Next, the compound (4-2) is reacted with a base or metal.

This reaction can be performed in the solvent used in the reaction forproviding the compound (4-2). Alternatively, it is acceptable to distillthe solvent from the solution containing the compound (4-2) and to add asolvent that is different from the solvent used in the reaction forproviding the compound (4-2), and then to react the compound (4-2) witha base or metal in this solvent.

The base may be either an organic base or an inorganic base. Preferredamong these are triethylamine, diisopropylethylamine, andtert-butoxypotassium.

The metal is preferably zinc.

The base or metal may be added to the solution containing the compound(4-2) which is collected after the reaction is quenched by adding wateror any appropriate substance. Alternatively, water or any appropriatesubstance and the base or metal may be added at the same time to asolution obtained by reacting the compound (4-1) and the halogenatingagent. In this case, the two steps can be successively performed in thesame container.

Then, the reaction can be quenched by adding an acidic aqueous solution.When the reaction between the compound (4-2) and the base or metal isperformed in a water-insoluble organic solvent, addition of the acidicaqueous solution to the reaction product causes separation of thesolution into two layers. A solution containing the compound (1) is thenobtained by collecting an organic layer by liquid separation.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the resultingsolution containing the compound (1), to filter out the desiccant andcollect the solution containing the compound (1) as a filtrate, and thento concentrate the solution.

The compound (1) can be highly purified by distilling the resultingsolution containing the compound (1) or sublimating the compound (1)from the solution. The purification technique is not limited todistillation or sublimation. If desired, the purification can beachieved by any known purification technique such as solvent extraction,drying, filtering, distillation, concentration, column chromatography,recrystallization, and any combination thereof.

A fourth production process includes reacting vinylene carbonate with acompound (5-1) represented by the following formula (5-1):Rf—X(wherein Rf is a C1-C8 fluorinated alkyl group; and X is a halogen atom)to provide a compound (5-2) represented by the following formula (5-2):

(wherein Rf is defined in the same manner as mentioned above; and X is ahalogen atom), and reacting the compound (5-2) with a base or metal toprovide a compound represented by the following formula (1):

(wherein Rf is defined in the same manner as mentioned above).

In other words, the fourth production process provides the targetfluorinated unsaturated cyclic carbonate by allowing a fluorinated alkylhalide to act on a known vinylene carbonate to provide a fluorinatedsaturated cyclic carbonate and the following dehydrohalogenation of theresulting fluorinated saturated cyclic carbonate. The fluorinatedsaturated cyclic carbonate obtained needs not to be isolated, and can bedirectly subjected to the dehydrohalogenation.

Rf in each of the formula (5-1) and the formula (5-2) is defined in thesame manner as Rf in the aforementioned formula (1).

X in each of the formula (5-1) and the formula (5-2) is a halogen atom,and is preferably a chlorine atom, a bromine atom, or an iodine atom,particularly preferably an iodine atom.

The reaction between the vinylene carbonate and the compound (5-1) maybe performed without a solvent or in a solvent. In the case of using asolvent in the reaction, the solvent may be either an organic solvent orwater. Preferred examples of the organic solvent include diethyl ether,tetrahydrofuran, ethylene glycol, hexane, benzene, toluene,benzotrifluoride, dimethylformamide, and dichloromethane. More preferredexamples thereof include benzene, toluene, benzotrifluoride,dimethylformamide, and dichloromethane. Still more preferred aretoluene, benzotrifluoride, and dichloromethane.

The reaction between the vinylene carbonate and the compound (5-1) canbe progressed by adding a radical initiator or by applying heat withouta radical initiator.

The radical initiator may be an organic radical initiator or may be aninorganic radical initiator.

The organic radical initiator is preferably an azo compound, an organicperoxide, or an organic metal compound. Preferred examples of the azocompound include 2,2′-azobis(isobutyronitrile),1,1′-azobis(cyclohexane-1-carbonitrile),1-[(1-cyano-1-methylethyl)azo]formamide, 4,4′-azobis(4-cyanovalericacid), dimethyl-1,1′-azobis(1-cyclohexanecarboxylate),2,2′-azobis(N-butyl-2-methylpropionamide), and2,2′-azobis(N-cyclohexyl-2-methylpropionamide). Preferred examples ofthe organic peroxide include dibenzoyl peroxide,di-(3-methylbenzoyl)peroxide, benzoyl(3-methylbenzoyl)peroxide,1,1-di(t-hexylperoxy)-3,3,5-trimethylcyclohexane,1,1-di(t-hexylperoxy)cyclohexane,1,1-di(t-butylperoxy)-2-methylcyclohexane,1,1-di(t-butylperoxy)cyclohexane, 2,2-di(t-butylperoxy)butane,t-butylcumyl peroxide, di-t-hexyl peroxide, di-t-butyl peroxide,1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate,t-hexylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylhexanoate,t-hexylperoxyisopropylmonocarbonate,t-butylperoxyisopropylmonocarbonate,t-butylperoxy-2-ethylhexylmonocarbonate, and2,5-dimethyl-2,5-di(benzoylperoxy)hexane. Preferred examples of theorganic metal compound include triethylborane, diethylzinc, andtrimethylaluminum.

The inorganic radical initiator may be a simple metal, a metal salt, ora like substance. Preferred examples of the simple metal include zinc,copper, and silver. The reaction may be performed in the presence ofmultiple simple metals. Examples of the metal salt include Na₂S₂O₃,Na₂S₂O₄, CuF, CuCl, CuBr, CuI, FeCl₂, FeBr₂, FeSO₄, Fe (acac)₂, AgF,AgCl, AgBr, and AgI. More preferred are Na₂S₂O₃, Na₂S₂O₄, CuBr, CuI,FeBr₂, FeSO₄, Fe (acac)₂, AgF, and AgCl. The reaction may be performedin the presence of multiple metal salts.

In the case of using a radical initiator, the reaction between thevinylene carbonate and the compound (5-1) is preferably performed at 0°C. to 200° C., more preferably 20° C. to 150° C. In the case of heatingwithout a radical initiator, the reaction temperature is preferably 150°C. to 300° C., more preferably 200° C. to 250° C.

When the reaction between the vinylene carbonate and the compound (5-1)is performed without a solvent or in an organic solvent, addition ofwater or any appropriate substance to the reaction product causesseparation of the solution into two layers. A solution containing thecompound (5-2) can be then obtained by collecting an organic layer byliquid separation. When the reaction is performed in water, addition ofa water-insoluble organic solvent to the reaction product causesseparation of the solution into two layers. A solution containing thecompound (5-2) can be then obtained by collecting an organic layer byliquid separation. When the reaction is performed without a solvent, asolution containing the compound (5-2) can be obtained by removingexcessive organic compounds with an evaporator, for example.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the solutioncontaining the compound (5-2), and to filter out the desiccant andcollect the solution containing the compound (5-2) as a filtrate. Thissolution may be subjected to the next step.

Next, the compound (5-2) is reacted with a base or metal.

This reaction can be performed in a solvent. The solvent may be anyorganic solvent, and may be the solvent used in the reaction forproviding the compound (5-2). Alternatively, it is acceptable to distillthe solvent from the solution containing the compound (5-2) and to add asolvent that is different from the solvent used in the reaction forproviding the compound (5-2)), and then to react the compound (5-2) witha base or metal in this solvent. Also, it is acceptable, afterperforming the reaction for providing the compound (5-2) without asolvent, to distill off volatile components in the reaction solution asappropriate and to introduce a solvent required, and then to react thecompound (5-2) with a base or metal in this solvent.

The base may be either an organic base or an inorganic base. Preferredamong these are triethylamine, diisopropylethylamine, andtert-butoxypotassium.

The metal is preferably zinc.

The base or metal may be added to the solution containing the compound(5-2) which is collected after the reaction is quenched by adding wateror any appropriate substance. Alternatively, water or any appropriatesubstance and the base or metal may be added at the same time to asolution obtained by reacting the vinylene carbonate and the compound(5-1). In this case, the two steps can be successively performed in thesame container.

Then, the reaction can be quenched by adding an acidic aqueous solution.When the reaction between the compound (5-2) and the base or metal isperformed in a water-insoluble organic solvent, addition of the acidicaqueous solution to the reaction product causes separation of thesolution into two layers. A solution containing the compound (1) is thenobtained by collecting an organic layer by liquid separation.

It is acceptable to add a desiccant such as magnesium sulfate, a hydrateof sodium sulfate (mirabilite), or molecular sieve to the resultingsolution containing the compound (1), to filter out the desiccant andcollect the solution containing the compound (1) as a filtrate, and thento concentrate the solution.

The compound (1) can be highly purified by distilling the resultingsolution containing the compound (1) or sublimating the compound (1)from the solution. The purification technique is not limited todistillation or sublimation. If desired, the purification can beachieved by any known purification technique such as solvent extraction,drying, filtering, concentration, column chromatography,recrystallization, and any combination thereof.

The aforementioned novel compound is useful as a component constitutingan electrolyte solution to be used in an electrochemical device such asa lithium ion secondary battery.

The electrolyte solution preferably contains the compound represented bythe formula (1), more preferably further contains a solvent and anelectrolyte salt. The electrolyte solution containing the compoundrepresented by the formula (1) has a high capacity recovery andgenerates a small amount of gas even when stored at high temperature.

The electrolyte solution preferably contains 0.001 to 90 vol % of thecompound represented by the formula (1) relative to the solvent. Theamount of the compound represented by the formula (1) is more preferably0.01 vol % or more while more preferably 60 vol % or less, still morepreferably 20 vol % or less, particularly preferably 10 vol % or less.

The solvent preferably further contains at least one selected from thegroup consisting of fluorinated acyclic carbonates, non-fluorinatedsaturated cyclic carbonates, fluorinated saturated cyclic carbonates,and non-fluorinated acyclic carbonates.

The fluorinated acyclic carbonates are each an acyclic carbonatecontaining a fluorine atom.

The fluorinated acyclic carbonate preferably has a fluorine content of10 to 70 mass %. The fluorine content may be calculated by:{(number of fluorine atoms×19)/(molecular weight of fluorinated acycliccarbonate)}×100(%)based on the structural formula of the fluorinated acyclic carbonate.

Examples of the fluorinated acyclic carbonate include fluorinatedacyclic carbonates represented by the formula: Rf¹OCOORf², where Rf¹ andRf² are the same as or different from each other and are each a C1-C4alkyl group or fluorine-containing alkyl group, but at least one of Rf¹and Rf² is a C1-C4 fluorine-containing alkyl group.

Rf¹ and Rf² are the same as or different from each other and are each aC1-C4 alkyl group or a C1-C4 fluorine-containing alkyl group, but atleast one of Rf¹ and Rf² is a C1-C4 fluorine-containing alkyl group.

The above carbon number is preferably 1 to 3 in order to achieve goodcompatibility with the electrolyte solution.

Examples of Rf¹ include CF₃—, CF₃CF₂—, (CF₃)₂CH—, CF₃CH₂—, C₂F₅CH₂—,HCF₂CH₂—, HCF₂CF₂CH₂—, and CF₃CFHCF₂CH₂—. In order to achieve high flameretardance, good rate characteristics, and good oxidation resistance,CF₃CH₂— and HCF₂CH₂— are preferred.

Examples of Rf² include CF₃—, CF₃CF₂—, (CF₃)₂CH—, CF₃CH₂—, C₂F₅CH₂—,HCF₂CH₂—, HCF₂CF₂CH₂—, and CF₃CFHCF₂CH₂—. In order to achieve high flameretardance, good rate characteristics, and good oxidation resistance,CF₃CH₂— and HCF₂CH₂— are preferred.

Specific examples of the fluorinated acyclic carbonate includefluorinated acyclic carbonates such as CF₃CH₂OCOOCH₂CF₃, CF₃CH₂OCOOCH₃,CF₃CF₂CH₂OCOOCH₂CF₂CF₃, and CF₃CF₂CH₂OCOOCH₃. Examples thereof furtherinclude compounds disclosed in JP H06-21992 A, JP 2000-327634 A, and JP2001-256983 A. In order to achieve high effectiveness of suppressinggeneration of gas and improving the high-temperature storagecharacteristics, at least one compound selected from the groupconsisting of CF₃CH₂OCOOCH₂CF₃, CF₃CH₂OCOOCH₃, andCF₃CF₂CH₂OCOOCH₂CF₂CF₃ is preferred. The fluorine content is morepreferably 20 mass % or more, still more preferably 30 mass % or more,particularly preferably 33 mass % or more. The fluorine content is morepreferably 60 mass % or less, still more preferably 55 mass % or less.

Examples of the non-fluorinated saturated cyclic carbonates includeethylene carbonate (EC), propylene carbonate (PC), and butylenecarbonate.

In order to achieve a high permittivity and a suitable viscosity, thenon-fluorinated saturated cyclic carbonates are each preferably at leastone compound selected from the group consisting of ethylene carbonate,propylene carbonate, and butylene carbonate.

For the non-fluorinated saturated cyclic carbonate, one of the abovecompounds may be used or two or more thereof may be used in combination.

The fluorinated saturated cyclic carbonates are each a saturated cycliccarbonate with a fluorine atom attached thereto. Specific examplesthereof include a fluorinated saturated cyclic carbonate (A) representedby the following formula (A):

wherein X¹ to X⁴ are the same as or different from each other, and areeach a fluorinated alkyl group which may optionally contain —H, —CH₃,—F, or an ether bond, or a fluorinated alkoxy group which may optionallycontain an ether bond; at least one of X¹ to X⁴ is a fluorinated alkylgroup which may optionally contain —F or an ether bond, or a fluorinatedalkoxy group which may optionally contain an ether bond.

If the electrolyte solution contains the fluorinated saturated cycliccarbonate (A) and is applied to a lithium ion secondary battery, astable film is formed on the negative electrode so that side reactionsof the electrolyte solution on the negative electrode may sufficientlybe suppressed. As a result, significantly stable, excellent charge anddischarge characteristics can be achieved.

The term “ether bond” herein means a bond represented by —O—.

In order to achieve a good permittivity and oxidation resistance, one ortwo of X¹ to X⁴ in the formula (A) is/are preferably a fluorinated alkylgroup which may optionally contain —F or an ether bond or a fluorinatedalkoxy group which may optionally contain an ether bond.

In anticipation of a decrease in the viscosity at low temperatures, anincrease in the flash point, and improvement in the solubility of theelectrolyte salt, each of X¹ to X⁴ in the formula (A) is preferably —H,—F, a fluorinated alkyl group (a), a fluorinated alkyl group (b)containing an ether bond, or a fluorinated alkoxy group (c).

The fluorinated alkyl group (a) is an alkyl group in which at least onehydrogen atom is replaced by a fluorine atom. The fluorinated alkylgroup (a) preferably has a carbon number of 1 to 20, more preferably 2to 17, still more preferably 2 to 7, particularly preferably 2 to 5.

Too large a carbon number may cause poor low-temperature characteristicsand low solubility of the electrolyte salt. Too small a carbon numbermay cause low solubility of the electrolyte salt, low dischargeefficiency, and high viscosity, for example.

Examples of the fluorinated alkyl group (a) which has a carbon number of1 include CFH₂—, CF₂H—, and CF₃—.

In order to achieve good solubility of the electrolyte salt, preferredexamples of the fluorinated alkyl group (a) which has a carbon number of2 or greater include fluorinated alkyl groups represented by thefollowing formula (a-1):R¹—R²—  (a-1)wherein R¹ is an alkyl group which may optionally contain a fluorineatom and which has a carbon number of 1 or greater; R² is a C1-C3alkylene group which may optionally contain a fluorine atom; and atleast one of R¹ and R² contains a fluorine atom.

R¹ and R² each may further contain an atom other than the carbon atom,hydrogen atom, and fluorine atom.

R¹ is an alkyl group which may optionally contain a fluorine atom andwhich has a carbon number of 1 or greater. R¹ is preferably a C1-C16linear or branched alkyl group. The carbon number of R¹ is morepreferably 1 to 6, still more preferably 1 to 3.

Specific examples of the linear or branched alkyl group for R¹ includeCH₃—, CH₃CH₂—, CH₃CH₂CH₂—, CH₃CH₂CH₂CH₂—, and the groups represented bythe following formulas:

wherein the dashed lines each represent a bonding site.

If R¹ is a linear alkyl group containing a fluorine atom, examplesthereof include CF₃—, CF₃CH₂—, CF₃CF₂—, CF₃CH₂CH₂—, CF₃CF₂CH₂—,CF₃CF₂CF₂—, CF₃CH₂CF₂—, CF₃CH₂CH₂CH₂—, CF₃CF₂CH₂CH₂—, CF₃CH₂CF₂CH₂—,CF₃CF₂CF₂CH₂—, CF₃CF₂CF₂CF₂—, CF₃CF₂CH₂CF₂—, CF₃CH₂CH₂CH₂CH₂—,CF₃CF₂CH₂CH₂CH₂—, CF₃CH₂CF₂CH₂CH₂—, CF₃CF₂CF₂CH₂CH₂—, CF₃CF₂CF₂CF₂CH₂—,CF₃CF₂CH₂CF₂CH₂—, CF₃CF₂CH₂CH₂CH₂CH₂—, CF₃CF₂CF₂CF₂CH₂CH₂—,CF₃CF₂CH₂CF₂CH₂CH₂—, HCF₂—, HCF₂CH₂—, HCF₂CF₂—, HCF₂CH₂CH₂—,HCF₂CF₂CH₂—, HCF₂CH₂CF₂—, HCF₂CF₂CH₂CH₂—, HCF₂CH₂CF₂CH₂—,HCF₂CF₂CF₂CF₂—, HCF₂CF₂CH₂CH₂CH₂—, HCF₂CH₂CF₂CH₂CH₂—, HCF₂CF₂CF₂CF₂CH₂—,HCF₂CF₂CF₂CF₂CH₂CH₂—, FCH₂—, FCH₂CH₂—, FCH₂CF₂—, FCH₂CF₂CH₂—,FCH₂CF₂CF₂—, CH₃CF₂CH₂—, CH₃CF₂CF₂—, CH₃CH₂CH₂—, CH₃CF₂CH₂CF₂—,CH₃CF₂CF₂CF₂—, CH₃CH₂CF₂CF₂—, CH₃CF₂CH₂CF₂CH₂—, CH₃CF₂CF₂CF₂CH₂—,CH₃CF₂CF₂CH₂CH₂—, CH₃CH₂CF₂CF₂CH₂—, CH₃CF₂CH₂CF₂CH₂CH₂—, HCFClCF₂CH₂—,HCF₂CFClCH₂—, HCF₂CFClCF₂CFClCH₂—, and HCFClCF₂CFClCF₂CH₂—.

If R¹ is a branched alkyl group containing a fluorine atom, preferredexamples thereof include those represented by the following formulas:

(wherein the dashed lines each represent a bonding site). If the grouphas a branch represented by —CH₃ or —CF₃, for example, the viscosity islikely to be high. Thus, the number of such branches is more preferablysmall (one) or zero.

R² is a C1-C3 alkylene group which may optionally contain a fluorineatom. R² may be a linear or branched group. Examples of a minimumstructural unit constituting such a linear or branched alkylene groupare shown below. R² is constituted by one or combination of these units.

(i) Linear Minimum Structural Units

—CH₂—, —CHF—, —CF₂—, —CHCl—, —CFCl—, —CCl₂—

(ii) Branched Minimum Structural Units (the Dashed Lines in the FormulasEach Represent a Bonding Site)

Preferred among these exemplified units are Cl-free structural unitsbecause such units are not dehydrochlorinated by a base, and thus aremore stable.

If R² is a linear group, the group consists only of the above linearminimum structural unit, preferably —CH₂—, —CH₂CH₂—, or —CF₂—. In orderto further improve the solubility of the electrolyte salt, —CH₂— or—CH₂CH₂— is more preferred.

If R² is a branched group, the group includes at least one of the abovebranched minimum structural units. Preferred examples thereof includethose represented by the formula: —(CX^(a)X^(b))— (wherein X^(a) is H,F, CH₃, or CF₃; X^(b) is CH₃ or CF₃; if X^(b) is CF₃, X^(a) is H orCH₃). Such groups can further improve the solubility of the electrolytesalt.

Preferred examples of the fluorinated alkyl group (a) include CF₃CF₂—,HCF₂CF₂—, H₂CFCF₂—, CH₃CF₂—, CF₃CF₂CF₂—, HCF₂CF₂CF₂—, H₂CFCF₂CF₂—,CH₃CF₂CF₂—, and those represented by the following formulas:

wherein the dashed lines each represent a bonding site.

The fluorinated alkyl group (b) containing an ether bond is an alkylgroup which has an ether bond and in which at least one hydrogen atom isreplaced by a fluorine atom. The fluorinated alkyl group (b) containingan ether bond preferably has a carbon number of 2 to 17. Too large acarbon number may cause high viscosity of the fluorinated saturatedcyclic carbonate (A) and an increased number of fluorine-containinggroups. Thus, the solubility of the electrolyte salt may be poor due toreduction in the permittivity, and the compatibility with other solventsmay be poor. Accordingly, the carbon number of the fluorinated alkylgroup (b) containing an ether bond is preferably 2 to 10, morepreferably 2 to 7.

The alkylene group which constitutes the ether segment of thefluorinated alkyl group (b) containing an ether bond may be a linear orbranched alkylene group. Examples of a minimum structural unitconstituting such a linear or branched alkylene group are shown below.

(i) Linear Minimum Structural Units

—CH₂—, —CHF—, —CF₂—, —CHCl—, —CFCl—, —CCl₂—

(ii) Branched Minimum Structural Units (the Dashed Lines in the FormulasEach Represent a Bonding Site)

The alkylene group may be constituted by one of these minimum structuralunits alone, or may be constituted by multiple linear units (i), bymultiple branched units (ii), or by a combination of a linear unit (i)and a branched unit (ii). Preferred specific examples thereof will bementioned later.

Preferred among these exemplified units are Cl-free structural unitsbecause such units are not dehydrochlorinated by a base, and thus aremore stable.

Still more preferred examples of the fluorinated alkyl group (b)containing an ether bond include those represented by the followingformula (b-1):R³—(OR⁴)_(n1)—  (b-1)wherein R³ is preferably a C1-C6 alkyl group which may optionallycontain a fluorine atom; R⁴ is preferably a C1-C4 alkylene group whichmay optionally contain a fluorine atom; n1 is an integer of 1 to 3; andat least one of R³ and R⁴ contains a fluorine atom.

Examples of the groups for R³ and R⁴ include the following, and anyappropriate combination of these groups can provide the fluorinatedalkyl group (b) containing an ether bond represented by the formula(b-1). Still, the groups are not limited thereto.

(1) R³ is preferably an alkyl group represented by the formula: X^(c)₃C—(R⁵)_(n2-), where three X^(c)s are the same as or different from eachother, and are each H or F; R⁵ is a C1-C5 alkylene group which mayoptionally contain a fluorine atom; and n2 is 0 or 1.

If n2 is 0, R³ may be CH₃—, CF₃—, HCF₂—, or H₂CF—, for example.

If n2 is 1, specific examples of a linear group for R³ include CF₃CH₂—,CF₃CF₂—, CF₃CH₂CH₂—, CF₃CF₂CH₂—, CF₃CF₂CF₂—, CF₃CH₂CF₂—, CF₃CH₂CH₂CH₂—,CF₃CF₂CH₂CH₂—, CF₃CH₂CF₂CH₂—, CF₃CF₂CF₂CH₂—, CF₃CF₂CF₂CF₂—,CF₃CF₂CH₂CF₂—, CF₃CH₂CH₂CH₂CH₂—, CF₃CF₂CH₂CH₂CH₂—, CF₃CH₂CF₂CH₂CH₂—,CF₃CF₂CF₂CH₂CH₂—, CF₃CF₂CF₂CF₂CH₂—, CF₃CF₂CH₂CF₂CH₂—,CF₃CF₂CH₂CH₂CH₂CH₂—, CF₃CF₂CF₂CF₂CH₂CH₂—, CF₃CF₂CH₂CF₂CH₂CH₂—, HCF₂CH₂—,HCF₂CF₂—, HCF₂CH₂CH₂—, HCF₂CF₂CH₂—, HCF₂CH₂CF₂—, HCF₂CF₂CH₂CH₂—,HCF₂CH₂CF₂CH₂—, HCF₂CF₂CF₂CF₂—, HCF₂CF₂CH₂CH₂CH₂—, HCF₂CH₂CF₂CH₂CH₂—,HCF₂CF₂CF₂CF₂CH₂—, HCF₂CF₂CF₂CF₂CH₂CH₂—, FCH₂CH₂—, FCH₂CF₂—,FCH₂CF₂CH₂—, FCH₂CF₂CH₂—, CH₃CF₂—, CH₃CH₂—, CH₃CF₂CH₂—, CH₃CF₂CF₂—,CH₃CH₂CH₂—, CH₃CF₂CH₂CF₂—, CH₃CF₂CF₂CF₂—, CH₃CH₂CF₂CF₂—, CH₃CH₂CH₂CH₂—,CH₃CF₂CH₂CF₂CH₂—, CH₃CF₂CF₂CF₂CH₂—, CH₃CF₂CF₂CH₂CH₂—, CH₃CH₂CF₂CF₂CH₂—,CH₃CH₂CF₂CF₂CH₂CH₂—, and CH₃CF₂CH₂CF₂CH₂CH₂—.

If n2 is 1, examples of a branched group for R³ include thoserepresented by the following formulas:

wherein the dashed lines each represent a bonding site.

If the group for R³ has a branch such as —CH₃ or —CF₃, the viscosity islikely to be high. Thus, the group for R³ is more preferably a lineargroup.

(2) In the segment —(OR⁴)_(n1)— of the formula (b-1), n1 is an integerof 1 to 3, preferably 1 or 2. If n1 is 2 or 3, R⁴s may be the same as ordifferent from each other.

Preferred specific examples of the group for R⁴ include the followinglinear or branched groups.

Examples of the linear groups include —CH₂—, —CHF—, —CF₂—, —CH₂CH₂—,—CF₂CH₂—, —CF₂CF₂—, —CH₂CF₂—, —CH₂CH₂CH₂—, —CH₂CH₂CF₂—, —CH₂CF₂CH₂—,—CH₂CF₂CF₂—, —CF₂CH₂CH₂—, —CF₂CF₂CH₂—, —CF₂CH₂CF₂—, and —CF₂CF₂CF₂—.

Examples of the branched groups include those represented by thefollowing formulas:

wherein the dashed lines each represent a bonding site.

The fluorinated alkoxy group (c) is an alkoxy group in which at leastone hydrogen atom is replaced by a fluorine atom. The fluorinated alkoxygroup (c) preferably has a carbon number of 1 to 17. The carbon numberis more preferably 1 to 6.

The fluorinated alkoxy group (c) is particularly preferably afluorinated alkoxy group represented by the formula: X^(d)₃C—(R⁶)_(n3)—O— (wherein three X^(d)s are the same as or different fromeach other, and are each H or F; R⁶ is preferably a C1-C5 alkylene groupwhich may optionally contain a fluorine atom; n3 is 0 or 1; and any ofthe three X^(d)s contains a fluorine atom).

Specific examples of the fluorinated alkoxy group (c) includefluorinated alkoxy groups in which an oxygen atom is bonded to an end ofthe alkyl group for R¹ in the formula (a-1).

The fluorinated alkyl group (a), the fluorinated alkyl group (b)containing an ether bond, and the fluorinated alkoxy group (c) in thefluorinated saturated cyclic carbonate (A) each preferably have afluorine content of 10 mass % or more. Too low a fluorine content mayfail to sufficiently achieve an effect of increasing the flash point.Thus, the fluorine content is more preferably 20 mass % or more, stillmore preferably 30 mass % or more. The upper limit thereof is usually 85mass %.

The fluorine content of each of the fluorinated alkyl group (a), thefluorinated alkyl group (b) containing an ether bond, and thefluorinated alkoxy group (c) is a value calculated by:{(Number of fluorine atoms×19)/(formula weight of the group)}×100(%)based on the corresponding structural formula.

In order to achieve a good permittivity and oxidation resistance, thefluorine content in the whole fluorinated saturated cyclic carbonate (A)is preferably 5 mass % or more, more preferably 10 mass % or more. Theupper limit thereof is usually 76 mass %.

The fluorine content in the whole fluorinated saturated cyclic carbonate(A) is a value calculated by:{(Number of fluorine atoms×19)/(molecular weight of fluorinatedsaturated cyclic carbonate (A))}×100(%)based on the structural formula of the fluorinated saturated cycliccarbonate (A).

Specific examples of the fluorinated saturated cyclic carbonate (A)include the following.

Those represented by the following formulas:

may be mentioned as specific examples of the fluorinated saturatedcyclic carbonate (A) represented by the formula (A) in which at leastone of X¹ to X⁴ is —F. These compounds have a high withstand voltage andgive good solubility of the electrolyte salt.

Alternatively, those represented by the following formulas:

may also be used.

Those represented by the following formulas:

may be mentioned as specific examples of the fluorinated saturatedcyclic carbonate (A) represented by the formula (A) in which at leastone of X¹ to X⁴ is a fluorinated alkyl group (a) and the others thereofare —H.

Those represented by the following formulas:

may be mentioned as specific examples of the fluorinated saturatedcyclic carbonate (A) represented by the formula (A) in which at leastone of X¹ to X⁴ is a fluorinated alkyl group (b) containing an etherbond or a fluorinated alkoxy group (c) and the others thereof are —H.

The fluorinated saturated cyclic carbonate (A) is not limited to theabove specific examples. One of the above fluorinated saturated cycliccarbonates (A) may be used alone, or two or more thereof may be used inany combination at any ratio. A preferred amount of the fluorinatedsaturated cyclic carbonate will be mentioned later, and such a preferredamount corresponds to a preferred amount of the fluorinated saturatedcyclic carbonate (A).

Preferred as the fluorinated saturated cyclic carbonate (A) arefluoroethylene carbonate and difluoroethylene carbonate.

Examples of the non-fluorinated acyclic carbonate include hydrocarbonacyclic carbonates such as CH₃OCOOCH₃ (dimethyl carbonate: DMC),CH₃CH₂OCOOCH₂CH₃ (diethyl carbonate: DEC), CH₃CH₂OCOOCH₃ (ethyl methylcarbonate: EMC), CH₃OCOOCH₂CH₂CH₃ (methyl propyl carbonate), methylbutyl carbonate, ethyl propyl carbonate, and ethyl butyl carbonate.Preferred among these is at least one compound selected from the groupconsisting of dimethyl carbonate, ethyl methyl carbonate, diethylcarbonate, methyl propyl carbonate, methyl butyl carbonate, ethyl propylcarbonate, and ethyl butyl carbonate.

The solvent preferably contains 10 to 99.99 vol %, more preferably 40vol % or more, still more preferably 50 vol % or more, particularlypreferably 70 vol % or more, while more preferably 99.9 vol % or less,still more preferably 99.5 vol % or less, further more preferably 99 vol% or less, particularly preferably 96 vol % or less, most preferably 80vol % or less, in total of the non-fluorinated saturated cycliccarbonate, fluorinated saturated cyclic carbonate, non-fluorinatedacyclic carbonate, and fluorinated acyclic carbonate.

The solvent preferably contains at least one saturated cyclic carbonateselected from the group consisting of non-fluorinated saturated cycliccarbonates and fluorinated saturated cyclic carbonates and at least oneacyclic carbonate selected from the group consisting of non-fluorinatedacyclic carbonates and fluorinated acyclic carbonates.

The volume ratio of the saturated cyclic carbonate and the acycliccarbonate is preferably 10/90 to 90/10, more preferably 30/70 or higher,while more preferably 70/30 or lower.

The electrolyte solution contains an electrolyte salt.

Any electrolyte salt usable for electrolyte solutions forelectrochemical devices such as secondary batteries and electricdouble-layer capacitors may be used. Preferred is a lithium salt.

Examples of the lithium salt include inorganic lithium salts such asLiClO₄, LiPF₆, and LiBF₄; and fluoroorganic acid lithium salts such asLiSO₃CF₃, LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, LiN(SO₂CF₃)(SO₂C₄F₉),LiC(SO₂CF₃)₃, LiPF₄(CF₃)₂, LiPF₄(C₂F₅)₂, LiPF₄(SO₂CF₃)₂,LiPF₄(SO₂C₂F₅)₂, LiBF₂(CF₃)₂, LiBF₂(C₂F₅)₂, LiBF₂(SO₂CF₃)₂,LiBF₂(SO₂C₂F₅)₂, lithium difluoro(oxalato)borate, lithiumbis(oxalato)borate, and salts represented by the formula:LiPF_(a)(C_(n)F_(2n+1))_(6-a) (wherein a is an integer of 0 to 5; and nis an integer of 1 to 6). These may be used alone or in combination oftwo or more.

In order to suppress degradation of the electrolyte solution afterhigh-temperature storage, the lithium salt is particularly preferably atleast one selected from the group consisting of LiPF₆, LiBF₄, LiSO₃CF₃,LiN(SO₂CF₃)₂, LiN(SO₂C₂F₅)₂, lithium difluoro(oxalato)borate, lithiumbis(oxalato)borate, and salts represented by the formula:LiPF_(a)(C_(n)F_(2n+1))_(6-a), where a is an integer of 0 to 5; and n isan integer of 1 to 6.

Examples of the salts represented by the formula:LiPF_(a)(C_(n)F_(2n+1))_(6-a) include LiPF₃(CF₃)₃, LiPF₃(C₂F₅)₃,LiPF₃(C₃F₇)₃, LiPF₃(C₄F₉)₃, LiPF₄(CF₃)₂, LiPF₄(C₂F₅)₂, LiPF₄(C₃F₇)₂, andLiPF₄(C₄F₉)₂, where the alkyl group represented by C₃F₇ or C₄F₉ in theformula may be either linear or branched.

The concentration of the electrolyte salt in the electrolyte solution ispreferably 0.5 to 3 mol/L. If the concentration thereof is outside thisrange, the electrolyte solution tends to have a low electricconductivity and the battery performance tends to be impaired.

The concentration of the electrolyte salt is more preferably 0.9 mol/Lor more and 1.5 mol/L or less.

The electrolyte salt is preferably an ammonium salt.

Examples of the ammonium salt include the following salts (IIa) to(IIe).

(IIa) Tetraalkyl Quaternary Ammonium Salts

Preferred examples thereof include tetraalkyl quaternary ammonium saltsrepresented by the following formula (IIa):

(wherein R^(1a), R^(2a), R^(3a), and R^(4a) are the same as or differentfrom each other, and are each a C1-C6 alkyl group which may optionallycontain an ether bond; and X⁻ is an anion). In order to improve theoxidation resistance, part or all of the hydrogen atoms in the ammoniumsalt may also preferably be replaced by a fluorine atom and/or a C1-C4fluorine-containing alkyl group.

Preferred specific examples of the tetraalkyl quaternary ammonium saltsinclude tetraalkyl quaternary ammonium salts represented by thefollowing formula (IIa-1):(R^(1a))_(x)(R^(2a))_(y)N^(⊕)X^(⊖)  (IIa-1)(wherein R^(1a), R^(2a), and X⁻ are defined in the same manner asmentioned above; x and y are the same as or different from each other,and are each an integer of 0 to 4, where x+y=4), and alkyl ethergroup-containing trialkyl ammonium salts represented by the followingformula (IIa-2):

(wherein R^(5a) is a C1-C6 alkyl group; R^(6a) is a C1-C6 divalenthydrocarbon group; R^(7a) is a C1-C4 alkyl group; z is 1 or 2; and X⁻ isan anion). Introduction of an alkyl ether group may lead to reduction inthe viscosity.

The anion X⁻ may be either an inorganic anion or an organic anion.Examples of the inorganic anion include AlCl₄ ⁻, BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻,TaF₆ ⁻, I⁻, and SbF₆ ⁻. Examples of the organic anion include CF₃COO⁻,CF₃SO₃ ⁻, (CF₃SO₂)₂N⁻, and (C₂F₅SO₂)₂N⁻.

In order to achieve good oxidation resistance and ionic dissociation,BF₄ ⁻, PF₆ ⁻, AsF₆ ⁻, and SbF₆ ⁻ are preferred.

Preferred specific examples of the tetraalkyl quaternary ammonium saltsinclude Et₄NBF₄, Et₄NClO₄, Et₄NPF₆, Et₄NAsF₆, Et₄NSbF₆, Et₄NCF₃SO₃,Et₄N(CF₃SO₂)₂N, Et₄NC₄F₉SO₃, Et₃MeNBF₄, Et₃MeNClO₄, Et₃MeNPF₆,Et₃MeNAsF₆, Et₃MeNSbF₆, Et₃MeNCF₃SO₃, Et₃MeN(CF₃SO₂)₂N, Et₃MeNC₄F₉SO₃,and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium salts. Particularlypreferred examples thereof include Et₄NBF₄, Et₄NPF₆, Et₄NSbF₆, Et₄NAsF₆,Et₃MeNBF₄, and N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium salts.

(IIb) Spirocyclic Bipyrrolidinium Salts

Preferred examples thereof include spirocyclic bipyrrolidinium saltsrepresented by the following formula (IIb-1):

(wherein R_(8a) and R^(9a) are the same as or different from each other,and are each a C1-C4 alkyl group; X⁺ is an anion; n1 is an integer of 0to 5; and n2 is an integer of 0 to 5); spirocyclic bipyrrolidinium saltsrepresented by the following formula (IIb-2):

(wherein R^(10a) and R^(11a) are the same as or different from eachother, and are each a C1-C4 alkyl group; X⁻ is an anion; n3 is aninteger of 0 to 5; and n4 is an integer of 0 to 5); and spirocyclicbipyrrolidinium salts represented by the following formula (IIb-3):

(wherein R^(12a) and R^(13a) are the same as or different from eachother, and are each a C1-C4 alkyl group; X⁻ is an anion; n5 is aninteger of 0 to 5; and n6 is an integer of 0 to 5). In order to improvethe oxidation resistance, part or all of the hydrogen atoms in thespirocyclic bipyrrolidinium salt may also preferably be replaced by afluorine atom and/or a C1-C4 fluorine-containing alkyl group.

Preferred specific examples of the anion X⁻ are the same as thosementioned for the salts (IIa). In order to achieve good dissociation anda low internal resistance under high voltage, BF₄ ⁻, PF₆ ⁻, (CF₃SO₂)₂N⁻,or (C₂F₅SO₂)₂N⁻ is preferred.

For example, those represented by the following formulas:

may be mentioned as preferred specific examples of the spirocyclicbipyrrolidinium salts.

These spirocyclic bipyrrolidinium salts have excellent solubility in asolvent, oxidation resistance, and ion conductivity.

(IIc) Imidazolium Salts

Preferred examples thereof include imidazolium salts represented by thefollowing formula (IIc):

(wherein R^(14a) and R^(15a) are the same as or different from eachother, and are each a C1-C6 alkyl group; and X⁻ is an anion). In orderto improve the oxidation resistance, part or all of the hydrogen atomsin the imidazolium salt may also preferably be replaced by a fluorineatom and/or a C1-C4 fluorine-containing alkyl group.

Preferred specific examples of the anion X⁻ are the same as thosementioned for the salts (IIa).

For example, those represented by the following formula:

may be mentioned as a preferred specific example of the imidazoliumsalts.

This imidazolium salt is excellent in that it has low viscosity and goodsolubility.

(IId): N-Alkylpyridinium Salts

Preferred examples thereof include N-alkylpyridinium salts representedby the following formula (IId):

(wherein R^(16a) is a C1-C6 alkyl group; and X⁻ is an anion). In orderto improve the oxidation resistance, part or all of the hydrogen atomsin the N-alkylpyridinium salt may also preferably be replaced by afluorine atom and/or a C1-C4 fluorine-containing alkyl group.

Preferred specific examples of the anion X⁻ are the same as thosementioned for the salts (IIa).

For example, those represented by the following formulas:

may be mentioned as preferred specific examples of the N-alkylpyridiniumsalts.

These N-alkylpyridinium salts are excellent in that they have lowviscosity and good solubility.

(IIe) N,N-Dialkylpyrrolidinium Salts

Preferred examples thereof include N,N-dialkylpyrrolidinium saltsrepresented by the following formula (IIe):

(wherein R^(17a) and R^(18a) are the same as or different from eachother, and are each a C1-C6 alkyl group; and X⁻ is an anion). In orderto improve the oxidation resistance, part or all of the hydrogen atomsin the N,N-dialkylpyrrolidinium salt may also preferably be replaced bya fluorine atom and/or a C1-C4 fluorine-containing alkyl group.

Preferred specific examples of the anion X⁻ are the same as thosementioned for the salts (IIa).

For example, those represented by the following formulas:

may be mentioned as preferred specific examples of theN,N-dialkylpyrrolidinium salts.

These N,N-dialkylpyrrolidinium salts are excellent in that they have lowviscosity and good solubility.

Preferred among these ammonium salts are those represented by any of theformulas (IIa), (IIb), and (IIc) because they have good solubility,oxidation resistance, and ion conductivity. More preferred are thoserepresented by the following formulas:

wherein Me is a methyl group; Et is an ethyl group; and X⁻, x, and y aredefined in the same manner as in the formula (IIa-1).

Another lithium salt may be used as the electrolyte salt. Preferredexamples thereof include LiAsF₆, LiSbF₆, and LiN(SO₂C₂H₅)₂.

In order to further increase the capacity, a magnesium salt may be used.Preferred examples of the magnesium salt include Mg(ClO₄)₂ andMg(OOC₂H₅)₂.

If the electrolyte salt is any of the above ammonium salts, theconcentration thereof is preferably 0.6 mol/L or higher. If theconcentration thereof is lower than 0.6 mol/L, not only thelow-temperature characteristics may be poor but also the initialinternal resistance may be high. The concentration of the electrolytesalt is more preferably 0.9 mol/L or higher.

For good low-temperature characteristics, the upper limit of theconcentration is preferably 3.0 mol/L or lower, more preferably 2.0mol/L or lower.

If the ammonium salt is triethyl methyl ammonium tetrafluoroborate(TEMABF₄), the concentration thereof is preferably 0.8 to 1.9 mol/L inorder to achieve excellent low-temperature characteristics.

If the ammonium salt is spirobipyrrolidinium tetrafluoroborate (SBPBF₄),the concentration thereof is preferably 0.7 to 2.0 mol/L.

The electrolyte solution preferably further includes polyethylene oxidethat has a weight average molecular weight of 2000 to 4000 and contains—OH, —OCOOH, or —COOH at an end.

Containing such a compound improves the stability at the interfacesbetween the electrolyte solution and the respective electrodes, and thuscan improve the battery characteristics.

Examples of the polyethylene oxide include polyethylene oxide monool,polyethylene oxide carboxylate, polyethylene oxide diol, polyethyleneoxide dicarboxylate, polyethylene oxide triol, and polyethylene oxidetricarboxylate. These may be used alone or in combination of two ormore.

In order to achieve good battery characteristics, a mixture ofpolyethylene oxide monool and polyethylene oxide diol and a mixture ofpolyethylene oxide carboxylate and polyethylene oxide dicarboxylate arepreferred.

Polyethylene oxide having too small a weight average molecular weightmay be easily oxidatively decomposed. The weight average molecularweight is more preferably 3000 to 4000.

The weight average molecular weight can be determined in terms ofpolystyrene equivalent by gel permeation chromatography (GPC).

The amount of the polyethylene oxide is preferably 1×10⁻⁶ to 1×10⁻²mol/kg in the electrolyte solution. Too small an amount of thepolyethylene oxide may impair the battery characteristics.

The amount of the polyethylene oxide is more preferably 5×10⁻⁶ mol/kg ormore.

The electrolyte solution preferably further contains, as an additive, atleast one selected from the group consisting of unsaturated cycliccarbonates (excluding the compounds represented by the formula (1)),fluorinated saturated cyclic carbonates, and cyclic sulfonic acidcompounds. Containing any of these compounds suppresses degradation ofthe battery characteristics.

The unsaturated cyclic carbonates are each a cyclic carbonate having anunsaturated bond, i.e., a cyclic carbonate having at least onecarbon-carbon unsaturated bond in the molecule. Specific examplesthereof include vinylene carbonate compounds such as vinylene carbonate,methyl vinylene carbonate, ethyl vinylene carbonate, 4,5-dimethylvinylene carbonate, and 4,5-diethyl vinylene carbonate; and vinylethylene carbonate compounds such as 4-vinyl ethylene carbonate (VEC),4-methyl-4-vinyl ethylene carbonate, 4-ethyl-4-vinyl ethylene carbonate,4-n-propyl-4-vinyl ethylene carbonate, 5-methyl-4-vinyl ethylenecarbonate, 4,4-divinyl ethylene carbonate, 4,5-divinyl ethylenecarbonate, 4,4-dimethyl-5-methylene ethylene carbonate, and4,4-diethyl-5-methylene ethylene carbonate. Preferred among these isvinylene carbonate, 4-vinyl ethylene carbonate, 4-methyl-4-vinylethylene carbonate, or 4,5-divinyl ethylene carbonate, and particularlypreferred is vinylene carbonate or 4-vinyl ethylene carbonate.

The unsaturated cyclic carbonate may have any molecular weight that doesnot significantly deteriorate the performance of the electrolytesolution. The molecular weight is preferably 50 or higher and 250 orlower. The unsaturated cyclic carbonate having a molecular weight withinthis range is likely to ensure the solubility of the unsaturated cycliccarbonate in the electrolyte solution and to enable sufficientachievement of the performance of the electrolyte solution. Themolecular weight of the unsaturated cyclic carbonate is more preferably80 or higher, while more preferably 150 or lower.

The unsaturated cyclic carbonate may also be preferably a fluorinatedunsaturated cyclic carbonate.

The number of fluorine atoms in the fluorinated unsaturated cycliccarbonate may be any number that is 1 or greater. The number of fluorineatoms is usually 6 or smaller, preferably 4 or smaller, most preferably1 or 2.

Examples of the fluorinated unsaturated cyclic carbonate includefluorinated vinylene carbonate derivatives and fluorinated ethylenecarbonate derivatives substituted with a substituent containing anaromatic ring or a carbon-carbon double bond.

Examples of the fluorinated vinylene carbonate derivatives include4-fluorovinylene carbonate, 4-fluoro-5-methyl vinylene carbonate,4-fluoro-5-phenyl vinylene carbonate, 4-allyl-5-fluorovinylenecarbonate, and 4-fluoro-5-vinyl vinylene carbonate.

Examples of the fluorinated ethylene carbonate derivatives substitutedwith a substituent containing an aromatic ring or a carbon-carbon doublebond include 4-fluoro-4-vinyl ethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinyl ethylene carbonate,4-fluoro-5-allyl ethylene carbonate, 4,4-difluoro-4-vinyl ethylenecarbonate, 4,4-difluoro-4-allyl ethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allyl ethylene carbonate,4-fluoro-4,5-divinyl ethylene carbonate, 4-fluoro-4,5-diallyl ethylenecarbonate, 4,5-difluoro-4,5-divinyl ethylene carbonate,4,5-difluoro-4,5-diallyl ethylene carbonate, 4-fluoro-4-phenyl ethylenecarbonate, 4-fluoro-5-phenyl ethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, and 4,5-difluoro-4-phenyl ethylene carbonate.

The fluorinated unsaturated cyclic carbonate may have any molecularweight that does not significantly deteriorate the performance of theelectrolyte solution. The molecular weight is preferably 50 or higherand 500 or lower. The fluorinated unsaturated cyclic carbonate having amolecular weight within this range is likely to ensure the solubility ofthe fluorinated unsaturated cyclic carbonate in the electrolyte solutionand to enable sufficient achievement of the performance of theelectrolyte solution.

The unsaturated cyclic carbonates may be used alone or in anycombination of two or more at any ratio.

Examples of the fluorinated saturated cyclic carbonate include compoundsmentioned as examples of the fluorinated saturated cyclic carbonatesusable for the solvent.

Examples of the cyclic sulfonic acid compounds include 1,3-propanesultone, 1,4-butane sultone, 1-fluoro-1,3-propane sultone,2-fluoro-1,3-propane sultone, and 3-fluoro-1,3-propane sultone.

In order to improve the high-temperature characteristics, theelectrolyte solution preferably contains 1,3-propane sultone and/or1,4-butane sultone.

If at least one compound selected from the group consisting of theunsaturated cyclic carbonates, the fluorinated saturated cycliccarbonates, and the cyclic sulfonic acid compounds is used as anadditive, the amount thereof in the electrolyte solution is preferably0.1 to 10 mass %, more preferably 1 mass % or more, while morepreferably 5 mass % or less.

The electrolyte solution may further contain any other solvents oradditives such as a cyclic or acyclic carboxylate, an ether compound, anitrogen-containing compound, a boron-containing compound, an organicsilicon-containing compound, a fireproof agent (a flame retardant), asurfactant, an additive for increasing the permittivity, an improver forcycle characteristics and rate characteristics, and an overchargeinhibitor, to the extent that the performance of the electrolytesolution is not impaired.

Examples of the cyclic carboxylate include those having 3 to 12 carbonatoms in total in the structural formula. Specific examples thereofinclude gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone,and epsilon-caprolactone. Particularly preferred is gamma-butyrolactonebecause it can improve the battery characteristics owing to improvementin the degree of dissociation of lithium ions.

In general, the amount of the cyclic carboxylate is preferably 0.1 mass% or more, more preferably 1 mass % or more, in 100 mass % of theelectrolyte solution. The cyclic carboxylate in an amount within thisrange is likely to improve the electric conductivity of the electrolytesolution, and thus to improve the large-current dischargecharacteristics of an electrolyte battery. The amount of the cycliccarboxylate is also preferably 10 mass % or less, more preferably 5 mass% or less. Such an upper limit may make it easy to give a viscositywithin an appropriate range to the electrolyte solution, to avoid areduction in the electric conductivity, to suppress an increase in theresistance of the negative electrode, and to give large-currentdischarge characteristics within a favorable range to an electrolytebattery.

A fluorinated cyclic carboxylate (fluorolactone) may also suitably beused as the cyclic carboxylate. Examples of the fluorolactone includefluorolactones represented by the following formula (C):

wherein X¹⁵ to X²⁰ are the same as or different from each other, and areeach —H, —F, —Cl, —CH₃, or a fluorinated alkyl group; and at least oneof X¹⁵ to X²⁰ is a fluorinated alkyl group.

Examples of the fluorinated alkyl group for X¹⁵ to X²⁰ include —CFH₂,—CF₂H, —CF₃, —CH₂CF₃, —CF₂CF₃, —CH₂CF₂CF₃, and —CF(CF₃)₂. In order toachieve high oxidation resistance and an effect of improving the safety,—CH₂CF₃ and —CH₂CF₂CF₃ are preferred.

One of X¹⁵ to X²⁰ or a plurality thereof may be replaced by —H, —F, —Cl,—CH₃, or a fluorinated alkyl group only when at least one of X¹⁵ to X²⁰is a fluorinated alkyl group. In order to achieve good solubility of theelectrolyte salt, the number of substituents is preferably 1 to 3, morepreferably 1 or 2.

The substitution may be at any of the above sites in the fluorinatedalkyl group. In order to achieve a good synthesizing yield, thesubstitution site is preferably X¹⁷ and/or X¹⁸. In particular, X¹⁷ orX¹⁸ is preferably a fluorinated alkyl group, especially, —CH₂CF₃ or—CH₂CF₂CF₃. The substituent for X¹⁵ to X²⁰ other than the fluorinatedalkyl group is —H, —F, —Cl, or CH₃. In order to achieve good solubilityof the electrolyte salt, —H is preferred.

In addition to those represented by the above formula, the fluorolactonemay also be a fluorolactone represented by the following formula (D):

wherein one of A and B is CX²⁶X²⁷ (where X²⁶ and X²⁷ are the same as ordifferent from each other, and are each —H, —F, —Cl, —CF₃, —CH₃, or analkylene group in which a hydrogen atom may optionally be replaced by ahalogen atom and which may optionally has a hetero atom in the chain)and the other is an oxygen atom; Rf¹² is a fluorinated alkyl group orfluorinated alkoxy group which may optionally contain an ether bond; X²¹and X²² are the same as or different from each other, and are each —H,—F, —Cl, —CF₃, or CH₃; X²³ to X²⁵ are the same as or different from eachother, and are each —H, —F, —Cl, or an alkyl group in which a hydrogenatom may optionally be replaced by a halogen atom and which mayoptionally contain a hetero atom in the chain; and n=0 or 1.

Preferred examples of the fluorolactone represented by the formula (D)include 5-membered ring structures represented by the following formula(E):

(wherein A, B, Rf¹², X²¹, X²², and X²³ are defined in the same manner asin the formula (D)) because they are easily synthesized and have goodchemical stability. Further, in relation to the combination of A and B,fluorolactones represented by the following formula (F):

(wherein Rf¹², X²¹, X²², X²³, X²⁶, and X²⁷ are defined in the samemanner as in the formula (D)) and fluorolactones represented by thefollowing formula (G):

(wherein Rf¹², X²¹, X²², X²³, X²⁶, and X²⁷ are defined in the samemanner as in the formula (D)) may be mentioned.

In order to particularly achieve excellent characteristics such as ahigh permittivity and a high withstand voltage, and to improve thecharacteristics of the electrolyte solution in the present invention,for example, to achieve good solubility of the electrolyte salt and towell reduce the internal resistance, those represented by the followingformulas:

may be mentioned.

Containing a fluorinated cyclic carboxylate leads to effects of, forexample, improving the ion conductivity, improving the safety, andimproving the stability at high temperature.

Examples of the acyclic carboxylate include those having three to sevencarbon atoms in total in the structural formula. Specific examplesthereof include methyl acetate, ethyl acetate, n-propyl acetate,isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate,methyl propionate, ethyl propionate, n-propyl propionate, isopropylpropionate, n-butyl propionate, isobutyl propionate, t-butyl propionate,methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate,methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, andisopropyl isobutyrate.

In order to improve the ion conductivity owing to a reduction in theviscosity, preferred examples thereof include methyl acetate, ethylacetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethylpropionate, n-propyl propionate, isopropyl propionate, methyl butyrate,and ethyl butyrate.

Also, a fluorinated acyclic carboxylate may also suitably be used.Preferred examples of the fluorine-containing ester include fluorinatedacyclic carboxylates represented by the following formula (H):Rf¹⁰COORf¹¹  (H)(wherein Rf¹⁰ is a C1-C2 fluorinated alkyl group; and Rf¹¹ is a C1-C4fluorinated alkyl group) because they have high flame retardance, goodcompatibility with other solvents, and good oxidation resistance.

Examples of the group for Rf¹⁰ include CF₃—, CF₃CF₂—, HCF₂CF₂—, HCF₂—,CH₃CF₂—, and CF₃CH₂—. In order to achieve good rate characteristics,CF₃— and CF₃CF₂— are particularly preferred.

Examples of the group for Rf¹¹ include —CF₃, —CF₂CF₃, —CH(CF₃)₂,—CH₂CF₃, —CH₂CH₂CF₃, —CH₂CF₂CFHCF₃, —CH₂C₂F₅, —CH₂CF₂CF₂H, —CH₂CH₂C₂F₅,—CH₂CF₂CF₃, and —CH₂CF₂CF₂CF₃. In order to achieve good compatibilitywith other solvents, —CH₂CF₃, —CH(CF₃)₂, —CH₂C₂F₅, and —CH₂CF₂CF₂H areparticularly preferred.

Specifically, for example, the fluorinated acyclic carboxylate mayinclude one or two or more of CF₃C(═O)OCH₂CF₃, CF₃C(═O)OCH₂CH₂CF₃,CF₃C(═O)OCH₂C₂F₅, CF₃C(═O)OCH₂CF₂CF₂H, and CF₃C(═O)OCH(CF₃)₂. In orderto achieve good compatibility with other solvents and good ratecharacteristics, CF₃C(═O)OCH₂C₂F₅, CF₃C(═O)OCH₂CF₂CF₂H, CF₃C(═O)OCH₂CF₃,and CF₃C(═O)OCH(CF₃)₂ are particularly preferred.

The ether compound is preferably a C3-C10 acyclic ether or a C3-C6cyclic ether.

Examples of the C3-C10 acyclic ether include diethyl ether, di-n-butylether, dimethoxy methane, methoxy ethoxy methane, diethoxy methane,dimethoxy ethane, methoxy ethoxy ethane, diethoxy ethane, ethyleneglycol di-n-propyl ether, ethylene glycol di-n-butyl ether, anddiethylene glycol dimethyl ether.

The ether compound may suitably be a fluorinated ether.

One example of the fluorinated ether is a fluorinated ether (I)represented by the following formula (I):Rf¹³—O—Rf¹⁴  (I)(wherein Rf¹³ and Rf¹⁴ are the same as or different from each other, andare each a C1-C10 alkyl group or a C1-C10 fluorinated alkyl group; andat least one of Rf¹³ and Rf¹⁴ is a fluorinated alkyl group). Containingthe fluorinated ether (I) can improve the flame retardance of theelectrolyte solution, as well as improve the stability and safety athigh temperature under high voltage.

In the formula (I), at least one of Rf¹³ and Rf¹⁴ has only to be aC1-C10 fluorinated alkyl group. In order to further improve the flameretardance and the stability and safety at high temperature under highvoltage of the electrolyte solution, both Rf¹³ and Rf¹⁴ are preferably aC1-C10 fluorinated alkyl group. In this case, Rf¹³ and Rf¹⁴ may be thesame as or different from each other.

Preferably, Rf¹³ and Rf¹⁴ are the same as or different from each other,and Rf¹³ is a C3-C6 fluorinated alkyl group and Rf¹⁴ is a C2-C6fluorinated alkyl group.

If the sum of the carbon numbers of Rf¹³ and Rf¹⁴ is too small, thefluorinated ether may have too low a boiling point. Too large a carbonnumber of Rf¹³ or Rf¹⁴ may cause low solubility of the electrolyte salt,which may cause a bad influence on the compatibility with other solvent,and the viscosity may be high so that the rate characteristics(viscousness) may be poor. In order to achieve excellent ratecharacteristics and boiling point, advantageously, the carbon number ofRf¹³ is 3 or 4 and the carbon number of Rf¹⁴ is 2 or 3.

The fluorinated ether (I) preferably has a fluorine content of 40 to 75mass %. The fluorinated ether (I) having a fluorine content within thisrange may lead to particularly excellent balance between the flameretardance and the compatibility. The above range is also preferred forgood oxidation resistance and safety.

The lower limit of the fluorine content is more preferably 45 mass %,still more preferably 50 mass %, particularly preferably 55 mass %. Theupper limit thereof is more preferably 70 mass %, still more preferably66 mass %.

The fluorine content of the fluorinated ether (I) is a value calculatedby:{(number of fluorine atoms×19)/(molecular weight of fluorinated ether(I))}×100(%)based on the structural formula of the fluorinated ether (I).

Examples of the group for Rf¹³ include CF₃CF₂CH₂—, CF₃CFHCF₂—,HCF₂CF₂CF₂—, HCF₂CF₂CH₂—, CF₃CF₂CH₂CH₂—, CF₃CFHCF₂CH₂—, HCF₂CF₂CF₂CF₂—,HCF₂CF₂CF₂CH₂—, HCF₂CF₂CH₂CH₂—, and HCF₂CF(CF₃)CH₂—. Examples of thegroup for Rf¹⁴ include —CH₂CF₂CF₃, —CF₂CFHCF₃, —CF₂CF₂CF₂H, —CH₂CF₂CF₂H,—CH₂CH₂CF₂CF₃, —CH₂CF₂CFHCF₃, —CF₂CF₂CF₂CF₂H, —CH₂CF₂CF₂CF₂H,—CH₂CH₂CF₂CF₂H, —CH₂CF(CF₃)CF₂H, —CF₂CF₂H, —CH₂CF₂H, and —CF₂CH₃.

Specific examples of the fluorinated ether (I) includeHCF₂CF₂CH₂OCF₂CF₂H, CF₃CF₂CH₂OCF₂CF₂H, HCF₂CF₂CH₂OCF₂CFHCF₃,CF₃CF₂CH₂OCF₂CFHCF₃, C₆F₁₃OCH₃, C₆F₁₃OC₂H₅, CsF₁₇OCH₃, CsF₁₇OC₂H₅,CF₃CFHCF₂CH(CH₃)OCF₂CFHCF₃, HCF₂CF₂OCH(C₂H₅)₂, HCF₂CF₂OC₄H₉,HCF₂CF₂OCH₂CH(C₂H₅)₂, and HCF₂CF₂OCH₂CH(CH₃)₂.

In particular, those having HCF₂— or CF₃CFH— at one end or both ends canprovide a fluorinated ether (I) having excellent polarizability and ahigh boiling point. The boiling point of the fluorinated ether (I) ispreferably 67° C. to 120° C. It is more preferably 80° C. or higher,still more preferably 90° C. or higher.

Such a fluorinated ether (I) may include one or two or more ofCF₃CH₂OCF₂CFHCF₃, CF₃CF₂CH₂OCF₂CFHCF₃, HCF₂CF₂CH₂OCF₂CFHCF₃,HCF₂CF₂CH₂OCH₂CF₂CF₂H, CF₃CFHCF₂CH₂OCF₂CFHCF₃, HCF₂CF₂CH₂OCF₂CF₂H, andCF₃CF₂CH₂OCF₂CF₂H, for example.

In order to advantageously achieve a high boiling point, goodcompatibility with other solvents, and good solubility of theelectrolyte salt, the fluorinated ether (I) is preferably at least oneselected from the group consisting of HCF₂CF₂CH₂OCF₂CFHCF₃ (boilingpoint: 106° C.), CF₃CF₂CH₂OCF₂CFHCF₃ (boiling point: 82° C.),HCF₂CF₂CH₂OCF₂CF₂H (boiling point: 92° C.), and CF₃CF₂CH₂OCF₂CF₂H(boiling point: 68° C.), more preferably at least one selected from thegroup consisting of HCF₂CF₂CH₂OCF₂CFHCF₃ (boiling point: 106° C.) andHCF₂CF₂CH₂OCF₂CF₂H (boiling point: 92° C.).

Examples of the C3-C6 cyclic ether include 1,3-dioxane,2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, and fluorinatedcompounds thereof. Preferred are dimethoxy methane, diethoxy methane,ethoxy methoxy methane, ethylene glycol n-propyl ether, ethylene glycoldi-n-butyl ether, and diethylene glycol dimethyl ether because they havea high ability to solvate with lithium ions and improve the degree ofion dissociation. Particularly preferred are dimethoxy methane, diethoxymethane, and ethoxy methoxy methane because they have low viscosity andgive a high ion conductivity.

Examples of the nitrogen-containing compound include nitrile,fluorine-containing nitrile, carboxylic acid amide, fluorine-containingcarboxylic acid amide, sulfonic acid amide, and fluorine-containingsulfonic acid amide. Also, 1-methyl-2-pyrrolidinone,1-methyl-2-piperidone, 3-methyl-2-oxazolidinone,1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide may be used.

Examples of the boron-containing compound include borate esters such astrimethyl borate and triethyl borate, boric acid ethers, and alkylborates.

Examples of the organic silicon-containing compound include (CH₃)₄—Siand (CH₃)₃—Si—Si(CH₃)₃.

Examples of the fireproof agent (flame retardant) includeorganophosphates and phosphazene-based compounds. Examples of theorganophosphates include fluoroalkyl phosphates, non-fluoroalkylphosphates, and aryl phosphates. Particularly preferred are fluoroalkylphosphates because they can show a flame retardant effect even at asmall amount.

Specific examples of the fluoroalkyl phosphates include fluorodialkylphosphates disclosed in JP H11-233141 A, alkyl phosphates disclosed inJP H11-283669 A, and fluorotrialkyl phosphates.

Preferred as the fireproof agent (flame retardant) are (CH₃O)₃P═O and(CF₃CH₂O)₃P═O, for example.

The surfactant may be any of cationic surfactants, anionic surfactants,nonionic surfactants, and amphoteric surfactants. In order to achievegood cycle characteristics and rate characteristics, the surfactant ispreferably one containing a fluorine atom.

Preferred examples of such a surfactant containing a fluorine atominclude fluorine-containing carboxylic acid salts represented by thefollowing formula (J):Rf¹⁵COO-M⁺  (J)(wherein Rf¹⁵ is a C3-C10 fluorine-containing alkyl group which mayoptionally contain an ether bond; M⁺ is Li⁺, Na⁺, K⁺, or NHR′₃ ⁺ (whereR's are the same as or different from each other, and are each H or aC1-C3 alkyl group)), and fluorine-containing sulfonic acid saltsrepresented by the following formula (K):Rf¹⁶SO₃-M⁺  (K)(wherein Rf¹⁶ is a C3-C10 fluorine-containing alkyl group which mayoptionally contain an ether bond; M⁺ is Li⁺, Na⁺, K⁺, or NHR′₃ ⁺ (whereR's are the same as or different from each other, and are each H or aC1-C3 alkyl group)).

In order to reduce the surface tension of the electrolyte solutionwithout impairing the charge and discharge cycle characteristics, theamount of the surfactant is preferably 0.01 to 2 mass % in theelectrolyte solution.

Examples of the additive for increasing the permittivity includesulfolane, methyl sulfolane, γ-butyrolactone, γ-valerolactone,acetonitrile, and propionitrile.

Examples of the improver for cycle characteristics and ratecharacteristics include methyl acetate, ethyl acetate, tetrahydrofuran,and 1,4-dioxane.

In order to suppress burst or combustion of batteries in case ofovercharge, for example, the overcharge inhibitor is preferably anovercharge inhibitor having an aromatic ring. Examples of the overchargeinhibitor having an aromatic ring include aromatic compounds such ascyclohexyl benzene, biphenyl, alkyl biphenyl, terphenyl, partiallyhydrogenated terphenyl, t-butyl benzene, t-amyl benzene, diphenyl ether,benzofuran, dibenzofuran, dichloroaniline, and toluene; fluorinatedaromatic compounds such as hexafluorobenzene, fluorobenzene,2-fluorobiphenyl, o-cyclohexyl fluorobenzene, and p-cyclohexylfluorobenzene; and fluoroanisole compounds such as 2,4-difluoroanisole,2,5-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole.Preferred are aromatic compounds such as biphenyl, alkyl biphenyl,terphenyl, partially hydrogenated terphenyl, cyclohexyl benzene, t-butylbenzene, t-amyl benzene, diphenyl ether, and dibenzofuran. Thesecompounds may be used alone or in combination of two or more. In thecase of combination use of two or more compounds, in order to achievegood balance between the overcharge inhibiting characteristics and thehigh-temperature storage characteristics, preferred are a combination ofcyclohexyl benzene and t-butyl benzene or t-amyl benzene, and acombination of at least one oxygen-free aromatic compound selected frombiphenyl, alkyl biphenyl, terphenyl, partially hydrogenated terphenyl,cyclohexyl benzene, t-butyl benzene, t-amyl benzene, and the like, andat least one oxygen-containing aromatic compound selected from diphenylether, dibenzofuran, and the like.

In order to prevent burst or combustion of batteries in case ofovercharge, for example, the amount of the overcharge inhibitor ispreferably 0.1 to 5 mass % in the electrolyte solution.

The electrolyte solution may further contain other known assistants tothe extent that the performance of the electrolyte solution is notimpaired. Examples of such known assistants include carbonate compoundssuch as erythrinan carbonate, spiro-bis-dimethylene carbonate, andmethoxy ethyl-methyl carbonate; carboxylic anhydrides such as succinicanhydride, glutaric anhydride, maleic anhydride, citraconic anhydride,glutaconic anhydride, itaconic anhydride, diglycolic anhydride,cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylicdianhydride, and phenylsuccinic anhydride; spiro compounds such as2,4,8,10-tetraoxaspiro[5.5]undecane and3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane; sulfur-containingcompounds such as ethylene sulfite, methyl fluorosulfonate, ethylfluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate,busulfan, sulfolene, diphenyl sulfone, N,N-dimethyl methane sulfoneamide, N,N-diethyl methane sulfone amide, and like other chain sulfones,fluorine-containing chain sulfones, chain sulfonates,fluorine-containing chain sulfonates, cyclic sulfones,fluorine-containing cyclic sulfones, halides of sulfonic acid, andhalides of fluorine-containing sulfonic acid; and fluoroaromaticcompounds of hydrocarbon compounds, including heptane, octane, nonane,decane, and cycloheptane. These compounds may be used alone or incombination of two or more. These assistants can improve the capacityretention characteristics and the cycle characteristics afterhigh-temperature storage.

The electrolyte solution may be combined with a polymer material andthereby formed into a gel-like (plasticized), gel electrolyte solution.

Examples of such a polymer material include conventionally knownpolyethylene oxide and polypropylene oxide, modified products thereof(see JP H08-222270 A, JP 2002-100405 A); polyacrylate-based polymers,polyacrylonitrile, and fluororesins such as polyvinylidene fluoride andvinylidene fluoride-hexafluoropropylene copolymers (see JP H04-506726 T,JP H08-507407 T, JP H10-294131 A); and complexes of any of thesefluororesins and any hydrocarbon resin (see JP H11-35765 A, JP H11-86630A). In particular, polyvinylidene fluoride or a vinylidenefluoride-hexafluoropropylene copolymer is preferably used as a polymermaterial for gel electrolytes.

The electrolyte solution may also contain an ion conductive compounddisclosed in Japanese Patent Application No. 2004-301934.

This ion conductive compound is an amorphous fluoropolyether compoundhaving a fluorine-containing group at a side chain and is represented bythe following formula (1-1):A-(D)-B  (1-1)wherein D is represented by the following formula (2-1a):-(D1)_(n)-(FAE)_(m)-(AE)_(p)-(Y)_(q)—(2-1a)[wherein D1 is an ether unit having a fluoroether group at a side chainand is represented by the following formula (2a):

(wherein Rf is a fluoroether group which may optionally contain across-linkable functional group; and R¹⁰ is a group or a bond that linksRf and the main chain);FAE is an ether unit having a fluorinated alkyl group at a side chainand is represented by the following formula (2b):

(wherein Rfa is a hydrogen atom or a fluorinated alkyl group which mayoptionally contain a cross-linkable functional group; and R¹¹ is a groupor a bond that links Rfa and the main chain);AE is an ether unit represented by the following formula (2c):

(wherein R¹³ is a hydrogen atom, an alkyl group which may optionallycontain a cross-linkable functional group, an aliphatic cyclichydrocarbon group which may optionally contain a cross-linkablefunctional group, or an aromatic hydrocarbon group which may optionallycontain a cross-linkable functional group; and R¹² is a group or a bondthat links R¹³ and the main chain);Y is a unit having at least one selected from the following formulas(2d-1) to (2d-3):

n is an integer of 0 to 200;m is an integer of 0 to 200;p is an integer of 0 to 10000;q is an integer of 1 to 100;n+m is not 0; andthe bonding order of D1, FAE, AE, and Y is not specified]; andA and B are the same as or different from each other, and are each ahydrogen atom, an alkyl group which may optionally contain a fluorineatom and/or a cross-linkable functional group, a phenyl group which mayoptionally contain a fluorine atom and/or a cross-linkable functionalgroup, a —COOH group, —OR (where R is a hydrogen atom or an alkyl groupwhich may optionally contain a fluorine atom and/or a cross-linkablefunctional group), an ester group, or a carbonate group (if an end of Dis an oxygen atom, A and B each are none of a —COOH group, —OR, an estergroup, and a carbonate group).

The electrolyte solution may further contain any other additives, ifnecessary. Examples of such other additives include metal oxides andglass.

The electrolyte solution may be prepared by any method using theaforementioned components.

The electrolyte solution can be suitably applied to electrochemicaldevices such as secondary batteries.

Examples of the electrochemical devices include lithium ion secondarybatteries, capacitors (electric double-layer capacitors), radicalbatteries, solar cells (in particular, dye-sensitized solar cells), fuelcells, various electrochemical sensors, electrochromic elements,electrochemical switching elements, aluminum electrolytic capacitors,and tantalum electrolytic capacitors. Preferred are lithium ionsecondary batteries and electric double-layer capacitors.

In the following, a lithium ion secondary battery is described as anexample of the electrochemical devices or secondary batteries.

The lithium ion secondary battery includes a positive electrode, anegative electrode, and the aforementioned electrolyte solution.

<Positive Electrode>

The positive electrode is formed from a positive electrode mixturecontaining a positive electrode active material, which is a material ofthe positive electrode, and a current collector.

The positive electrode active material may be any material that canelectrochemically occlude and release lithium ions. For example, asubstance containing lithium and at least one transition metal ispreferred. Specific examples thereof include lithium-containingtransition metal complex oxides and lithium-containing transition metalphosphoric acid compounds. In particular, the positive electrode activematerial is preferably a lithium-containing transition metal complexoxide that generates a high voltage.

Examples of the lithium-containing transition metal complex oxidesinclude lithium-manganese spinel complex oxides represented by theformula (L): Li_(a)Mn_(2-b)M¹ _(b)O₄ (wherein 0.9≤a; 0≤b≤1.5; and M¹ isat least one metal selected from the group consisting of Fe, Co, Ni, Cu,Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge),

lithium-nickel complex oxides represented by the formula (M):LiNi_(1-c)M² _(c)O₂ (wherein 0≤c≤0.5; and M² is at least one metalselected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V,Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge), and

lithium-cobalt complex oxides represented by the formula (N):LiCo_(1-d)M³ _(d)O₂ (wherein 0≤d≤0.5; and M³ is at least one metalselected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V,Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge).

In order to provide a high-power lithium ion secondary battery having ahigh energy density, preferred is LiCoO₂, LiMnO₂, LiNiO₂, LiMn₂O₄,LiNi_(0.8)Co_(0.15)Al_(0.5)O₂, or LiNi_(1/3) Co_(1/3)Mn_(1/3)O₂.

Examples of other positive electrode active materials include LiFePO₄,LiNi_(0.8)Co_(0.2)O₂, Li_(1.2)Fe_(0.4)Mn_(0.4)O₂, LiNi_(0.5)Mn_(0.5)O₂,and LiV₃O₆.

In order to improve the continuous charge characteristics, the positiveelectrode active material preferably contains lithium phosphate. The useof lithium phosphate may be achieved in any manner, and the positiveelectrode active material and lithium phosphate are preferably used in amixed state. The lower limit of the amount of lithium phosphate in thesum of the amounts of the positive electrode active material and thelithium phosphate is preferably 0.1 mass % or more, more preferably 0.3mass % or more, still more preferably 0.5 mass % or more, whereas theupper limit thereof is preferably 10 mass % or less, more preferably 8mass % or less, still more preferably 5 mass % or less.

To the surface of the positive electrode active material may be attacheda substance having a composition different from the positive electrodeactive material. Examples of the substance attached to the surfaceinclude oxides such as aluminum oxide, silicon oxide, titanium oxide,zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimonyoxide, and bismuth oxide; sulfates such as lithium sulfate, sodiumsulfate, potassium sulfate, magnesium sulfate, calcium sulfate, andaluminum sulfate; carbonates such as lithium carbonate, calciumcarbonate, magnesium carbonate; and carbon.

Such a substance may be attached to the surface of the positiveelectrode active material by, for example, a method of dissolving orsuspending the substance in a solvent, impregnating the positiveelectrode active material with the solution or suspension, and dryingthe impregnated material; a method of dissolving or suspending aprecursor of the substance in a solvent, impregnating the positiveelectrode active material with the solution or suspension, and reactingthe material and the precursor by heating; or a method of adding thesubstance to a precursor of the positive electrode active material andsimultaneously sintering the materials. In the case of attaching carbon,a carbonaceous material in the form of activated carbon, for example,may be mechanically attached to the surface afterward.

The lower limit of the amount (in terms of mass) of the substanceattached to the surface relative to the amount of the positive electrodeactive material is preferably 0.1 ppm or more, more preferably 1 ppm ormore, still more preferably 10 ppm or more, whereas the upper limitthereof is preferably 20% or less, more preferably 10% or less, stillmore preferably 5% or less. The substance attached to the surface cansuppress the oxidation of the electrolyte solution on the surface of thepositive electrode active material, improving the battery life. Toosmall an amount thereof may fail to sufficiently provide the effect. Toolarge an amount thereof may hinder the entrance and exit of lithiumions, possibly increasing the resistance.

Particles of the positive electrode active material may have anyconventionally used shape, such as an agglomerative shape, a polyhedralshape, a spherical shape, an ellipsoidal shape, a plate shape, a needleshape, or a pillar shape. The primary particles may agglomerate to formsecondary particles.

The positive electrode active material has a tap density of preferably0.5 g/cm³ or higher, more preferably 0.8 g/cm³ or higher, still morepreferably 1.0 g/cm³ or higher. If the tap density of the positiveelectrode active material is below the lower limit, an increased amountof a dispersion medium is required, as well as increased amounts of aconductive material and a binder are required in formation of a positiveelectrode active material layer. Thus, the filling rate of the positiveelectrode active material into the positive electrode active materiallayer may be limited and the battery capacity may be limited. With acomplex oxide powder having a high tap density, a positive electrodeactive material layer with a high density can be formed. The tap densityis preferably as high as possible and has no upper limit, in general.Still, if the tap density is too high, diffusion of lithium ions in thepositive electrode active material layer with the electrolyte solutionserving as a diffusion medium may function as a rate-determining step,so that the load characteristics may be easily impaired. Thus, the upperlimit of the tap density is preferably 4.0 g/cm³ or lower, morepreferably 3.7 g/cm³ or lower, still more preferably 3.5 g/cm³ or lower.

The tap density is determined as a powder filling density (tap density)g/cm³ when 5 to 10 g of the positive electrode active material powder isfilled into a 10-ml glass graduated cylinder and the cylinder is tapped200 times with a stroke of about 20 mm.

The particles of the positive electrode active material have a mediansize d50 (if the primary particles agglomerate to form secondaryparticles, the secondary particle size) of preferably 0.3 μm or greater,more preferably 0.5 μm or greater, still more preferably 0.8 μm orgreater, most preferably 1.0 μm or greater, while preferably 30 μm orsmaller, more preferably 27 μm or smaller, still more preferably 25 μmor smaller, most preferably 22 μm or smaller. If the median size isbelow the lower limit, products with a high tap density may not beobtained. If the median size exceeds the upper limit, diffusion oflithium in the particles may take a long time, so that the batteryperformance may be poor or streaks may be formed in formation ofpositive electrodes for batteries, i.e., when the active material andcomponents such as a conductive material and a binder are formed intoslurry by adding a solvent and the slurry is applied in the form of afilm, for example. Mixing two or more positive electrode activematerials having different median sizes d50 leads to further improvedfilling in formation of positive electrodes.

The median size d50 is determined using a known laserdiffraction/scattering particle size distribution analyzer. In the caseof using LA-920 (Horiba, Ltd.) as the particle size distributionanalyzer, the dispersion medium used in the measurement is a 0.1 mass %sodium hexametaphosphate aqueous solution and the measurement refractiveindex is set to 1.24 after 5-minute ultrasonic dispersion.

If the primary particles agglomerate to form secondary particles, theaverage primary particle size of the positive electrode active materialis preferably 0.05 μm or greater, more preferably 0.1 μm or greater,still more preferably 0.2 μm or greater. The upper limit thereof ispreferably 5 μm or smaller, more preferably 4 μm or smaller, still morepreferably 3 μm or smaller, most preferably 2 μm or smaller. If theaverage primary particle size exceeds the upper limit, sphericalsecondary particles are difficult to form, which may have a badinfluence on the powder filling or may cause a great reduction in thespecific surface area. Thus, the battery performance such as outputcharacteristics is more likely to be impaired. In contrast, if theaverage primary particle size is below the lower limit, the crystalsusually do not sufficiently grow. Thus, charge and discharge may bepoorly reversible, for example.

The primary particle size is measured by scanning electron microscopic(SEM) observation. Specifically, the primary particle size is determinedas follows. First, a photograph at a magnification of 10000× is taken.Any 50 primary particles are selected and the maximum length between theleft and right boundary lines of each primary particle is measured alongthe horizontal line. Then, the average value of the maximum lengths iscalculated, which is defined as the primary particle size.

The positive electrode active material has a BET specific surface areaof preferably 0.1 m²/g or larger, more preferably 0.2 m²/g or larger,still more preferably 0.3 m²/g or larger, while preferably 50 m²/g orsmaller, more preferably 40 m²/g or smaller, still more preferably 30m²/g or smaller. If the BET specific surface area is smaller than theabove range, the battery performance may be easily impaired. If it islarger than the above range, the tap density is less likely to be highand formation of the positive electrode active material layer mayinvolve a difficulty in applying the material.

The BET specific surface area is defined by a value determined by singlepoint BET nitrogen adsorption utilizing a gas flow method using asurface area analyzer (e.g., fully automatic surface area measurementdevice, Ohkura Riken Co., Ltd.), a sample pre-dried in the stream ofnitrogen at 150° C. for 30 minutes, and a nitrogen-helium gas mixturewith the nitrogen pressure relative to the atmospheric pressure beingaccurately adjusted to 0.3.

When the lithium ion secondary battery is used as a large-size lithiumion secondary battery for hybrid vehicles or distributed generation, itis required to achieve a high output. Thus, the particles of thepositive electrode active material preferably mainly include secondaryparticles.

The particles of the positive electrode active material preferablyinclude 0.5 to 7.0 vol % of fine particles having an average secondaryparticle size of 40 μm or smaller and having an average primary particlesize of 1 μm or smaller. Containing fine particles having an averageprimary particle size of 1 μm or smaller leads to an increase in thecontact area with the electrolyte solution and more rapid diffusion oflithium ions between the electrode and the electrolyte solution. As aresult, the output performance of the battery can be improved.

The positive electrode active material can be produced by any usualmethod of producing inorganic compounds. In particular, a spherical orellipsoidal active material can be produced by various methods. Forexample, a material substance of transition metal is dissolved orcrushed and dispersed in a solvent such as water, and the pH of thesolution or dispersion is adjusted under stirring to form a sphericalprecursor. The precursor is recovered and, if necessary, dried. Then, aLi source such as LiOH, Li₂CO₃, or LiNO₃ is added thereto and themixture is sintered at high temperature, thereby providing an activematerial.

In order to produce a positive electrode, the aforementioned positiveelectrode active materials may be used alone or in any combination withone or more having different compositions at any ratio. Preferredexamples of the combination in this case include a combination of LiCoO₂and LiMn₂O₄ in which part of Mn may optionally be replaced by adifferent transition metal (e.g., LiNio_(0.33)Co_(0.33)Mn_(0.33)O₂), anda combination with LiCoO₂ in which part of Co may optionally be replacedby a different transition metal.

In order to achieve a high battery capacity, the amount of the positiveelectrode active material is preferably 50 to 99 mass %, more preferably80 to 99 mass %, of the positive electrode mixture. The amount of thepositive electrode active material in the positive electrode activematerial layer is preferably 80 mass % or more, more preferably 82 mass% or more, particularly preferably 84 mass % or more. The amount thereofis preferably 99 mass % or less, more preferably 98 mass % or less. Toosmall an amount of the positive electrode active material in thepositive electrode active material layer may lead to an insufficientelectric capacity. In contrast, too large an amount thereof may lead toan insufficient strength of the resulting positive electrode.

The positive electrode mixture preferably further contains a binder, athickening agent, and a conductive material.

The binder may be any material that is safe against a solvent to be usedin production of the electrode and against the electrolyte solution.Examples thereof include polyvinylidene fluoride,polytetrafluoroethylene, polyethylene, polypropylene, styrene-butadienerubber (SBR), isoprene rubber, butadiene rubber, ethylene-acrylic acidcopolymers, ethylene-methacrylic acid copolymers, polyethyleneterephthalate, polymethyl methacrylate, polyimide, aromatic polyamide,cellulose, nitro cellulose, acrylonitrile-butadiene rubber (NBR),fluororubber, ethylene-propylene rubber, styrene-butadiene-styrene blockcopolymers or hydrogenated products thereof, ethylene-propylene-dieneterpolymers (EPDM), styrene-ethylene-butadiene-ethylene copolymers,styrene-isoprene-styrene block copolymers or hydrogenated productsthereof, syndiotactic-1,2-polybutadiene, polyvinyl acetate,ethylene-vinyl acetate copolymers, propylene-α-olefin copolymers,fluorinated polyvinylidene fluoride, tetrafluoroethylene-ethylenecopolymers, and polymer compositions having an ion conductivity ofalkali metal ions (especially, lithium ions). These agents may be usedalone or in any combination of two or more at any ratio.

The amount of the binder, which is expressed as the proportion of thebinder in the positive electrode active material layer, is usually 0.1mass % or more, preferably 1 mass % or more, more preferably 1.5 mass %or more, while usually 80 mass % or less, preferably 60 mass % or less,still more preferably 40 mass % or less, most preferably 10 mass % orless. Too low a proportion of the binder may fail to sufficiently holdthe positive electrode active material so that the resulting positiveelectrode may have an insufficient mechanical strength, resulting inimpaired battery performance such as cycle characteristics. In contrast,too high a proportion thereof may lead to a reduction in batterycapacity and conductivity.

Examples of the thickening agent include carboxymethyl cellulose, methylcellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol,oxidized starch, monostarch phosphate, casein, and salts thereof. Theseagents may be used alone or in any combination of two or more at anyratio.

The proportion of the thickening agent relative to the active materialis usually 0.1 mass % or more, preferably 0.2 mass % or more, morepreferably 0.3 mass % or more, while usually 5 mass % or less,preferably 3 mass % or less, more preferably 2 mass % or less. If theproportion thereof is below this range, easiness of application may besignificantly impaired. If the proportion exceeds this range, theproportion of the active material in the positive electrode activematerial layer is low, so that the capacity of the battery may be low orthe resistance between the positive electrode active materials may behigh.

The conductive material may be any known conductive material. Specificexamples thereof include metal materials such as copper and nickel, andcarbon materials such as graphite (e.g., natural graphite, artificialgraphite), carbon black (e.g., acetylene black), and amorphous carbon(e.g., needle coke). These materials may be used alone or in anycombination of two or more at any ratio. The conductive material is usedsuch that the amount thereof in the positive electrode active materiallayer is usually 0.01 mass % or more, preferably 0.1 mass % or more,more preferably 1 mass % or more, while usually 50 mass % or less,preferably 30 mass % or less, more preferably 15 mass % or less. If theamount thereof is below this range, the conductivity may beinsufficient. In contrast, if the amount thereof is above this range,the battery capacity may be low.

The solvent for forming slurry may be any solvent that can dissolve ordisperse therein the positive electrode active material, the conductivematerial, and the binder, as well as a thickening agent that is used asnecessary. The solvent may be either an aqueous solvent or an organicsolvent. Examples of the aqueous medium include water and solventmixtures of an alcohol and water. Examples of the organic medium includealiphatic hydrocarbons such as hexane; aromatic hydrocarbons such asbenzene, toluene, xylene, and methyl naphthalene; heterocyclic compoundssuch as quinoline and pyridine; ketones such as acetone, methyl ethylketone, and cyclohexanone; esters such as methyl acetate and methylacrylate; amines such as diethylene triamine andN,N-dimethylaminopropylamine; ethers such as diethyl ether, propyleneoxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone(NMP), dimethylformamide, and dimethyl acetamide; and aprotic polarsolvents such as hexamethyl phosphramide and dimethyl sulfoxide.

Examples of the material of the current collector for positiveelectrodes include metal materials such as aluminum, titanium, tantalum,stainless steel, and nickel, and any alloy thereof; and any carbonmaterial such as carbon cloth and carbon paper. Preferred is a metalmaterial, especially aluminum or an alloy thereof.

In the case of a metal material, the current collector may be in theform of metal foil, metal cylinder, metal coil, metal plate, metal film,expanded metal, punched metal, metal foam, or the like. In the case of acarbon material, it may be in the form of carbon plate, carbon film,carbon cylinder, or the like. Preferred among these is a metal film. Thefilm may be in the form of mesh, as appropriate. The film may have anythickness, and the thickness is usually 1 μm or greater, preferably 3 μmor greater, more preferably 5 μm or greater, while usually 1 mm orsmaller, preferably 100 μm or smaller, more preferably 50 μm or smaller.If the film is thinner than this range, it may have an insufficientstrength as a current collector. In contrast, if the film is thickerthan this range, it may have poor handleability.

In order to reduce the electronic contact resistance between the currentcollector and the positive electrode active material layer, the currentcollector also preferably has a conductive aid applied on the surfacethereof. Examples of the conductive aid include carbon and noble metalssuch as gold, platinum, and silver.

The ratio between the thicknesses of the current collector and thepositive electrode active material layer may be any value, and the ratio((thickness of positive electrode active material layer on one sideimmediately before injection of electrolyte solution)/(thickness ofcurrent collector)) is preferably 20 or lower, more preferably 15 orlower, most preferably 10 or lower. The ratio is also preferably 0.5 orhigher, more preferably 0.8 or higher, most preferably 1 or higher. Ifthe ratio exceeds this range, the current collector may generate heatdue to Joule heating during high-current-density charge and discharge.If the ratio is below this range, the ratio by volume of the currentcollector to the positive electrode active material is so high that thecapacity of the battery may be low.

The positive electrode may be produced by a usual method. One example ofthe production method is a method in which the positive electrode activematerial is mixed with the aforementioned binder, thickening agent,conductive material, solvent, and other components to form a slurry-likepositive electrode mixture, and then this mixture is applied to acurrent collector, dried, and pressed so as to be densified.

The densification may be achieved using a manual press or a rollerpress, for example. The density of the positive electrode activematerial layer is preferably 1.5 g/cm³ or higher, more preferably 2g/cm³ or higher, still more preferably 2.2 g/cm³ or higher, whilepreferably 5 g/cm³ or lower, more preferably 4.5 g/cm³ or lower, stillmore preferably 4 g/cm³ or lower. If the density is above this range,the permeability of the electrolyte solution toward the vicinity of theinterface between the current collector and the active material may below, in particular, the charge and discharge characteristics at highcurrent density may be impaired, so that a high output may not beachieved. If the density is below this range, the conductivity betweenthe active materials may be low and the resistance of the battery mayincrease, so that a high output may not be achieved.

In the case of using the electrolyte solution, in order to improve thestability at high output and high temperature, the area of the positiveelectrode active material layer is preferably large relative to theouter surface area of an external case of the battery. Specifically, thesum of the areas of the positive electrodes is preferably 15 times ormore, more preferably 40 times or more, greater than the surface area ofthe external case of the secondary battery. For closed, square-shapedcases, the outer surface area of an external case of the battery hereinrefers to the total area calculated from the dimension of length, width,and thickness of the case portion into which a power-generating elementis filled except for the protruding portions of the terminals. Forclosed, cylinder-shaped cases, the outer surface area of an externalcase of the battery herein refers to a geometric surface area of anapproximated cylinder of the case portion into which a power-generatingelement is filled except for the protruding portion of the terminals.The sum of the areas of the positive electrodes herein refers to ageometric surface area of a positive electrode mixture layer opposite toa mixture layer including the negative electrode active material. Forstructures including a current collector foil and positive electrodemixture layers on both sides of the current collector, the sum of theareas of the positive electrodes is the sum of the areas calculated onthe respective sides.

The positive electrode plate may have any thickness. In order to achievea high capacity and a high output, the lower limit of the thickness ofthe mixture layer on one side of the current collector excluding thethickness of the base metal foil is preferably 10 μm or greater, morepreferably 20 μm or greater, while preferably 500 μm or smaller, morepreferably 450 μm or smaller.

To the surface of the positive electrode plate may be attached asubstance having a different composition. Examples of the substanceattached to the surface include oxides such as aluminum oxide, siliconoxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide,boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithiumsulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calciumsulfate, and aluminum sulfate; carbonates such as lithium carbonate,calcium carbonate, and magnesium carbonate; and carbon.

<Negative Electrode>

The negative electrode is formed from a negative electrode mixtureincluding a negative electrode active material, and a current collector.

Examples of the negative electrode active material include carbonaceousmaterial that can occlude and release lithium such as pyrolysates oforganic matter under various pyrolysis conditions, artificial graphite,and natural graphite; metal oxide material that can occlude and releaselithium such as tin oxide and silicon oxide; lithium metals; variouslithium alloys; and lithium-containing metal complex oxide material. Twoor more of these negative electrode active materials may be used in amixed state.

The carbonaceous material that can occlude and release lithium ispreferably artificial graphite produced by high-temperature treatment ofeasily graphitizable pitch from various materials, purified naturalgraphite, or material obtained by surface-treating such graphite withpitch or other organic matter and then carbonizing the surface-treatedgraphite. In order to achieve a good balance between the initialirreversible capacity and the high-current-density charge and dischargecharacteristics, it is more preferably one selected from carbonaceousmaterial obtained by one or more heat treatments at 400° C. to 3200° C.on natural graphite, artificial graphite, an artificial carbonaceoussubstance, or an artificial graphite substance; carbonaceous materialwhich allows the negative electrode active material layer to include atleast two or more carbonaceous matters having different crystallinitiesand/or to have an interface between the carbonaceous matters having thedifferent crystallinities; and carbonaceous material which allows thenegative electrode active material layer to have an interface between atleast two or more carbonaceous matters having different orientations.These carbonaceous materials may be used alone or in any combination oftwo or more at any ratio.

Examples of the carbonaceous material obtained by one or more heattreatments at 400° C. to 3200° C. on an artificial carbonaceoussubstance or an artificial graphite substance include coal-based coke,petroleum-based coke, coal-based pitch, petroleum-based pitch, and thoseprepared by oxidizing these pitches; needle coke, pitch coke, and carbonmaterial prepared by partially graphitizing these cokes; pyrolysates oforganic matter such as furnace black, acetylene black, and pitch-basedcarbon fibers; carbonizable organic matter and carbides thereof; andsolutions prepared by dissolving carbonizable organic matter in alow-molecular-weight organic solvent such as benzene, toluene, xylene,quinoline, or n-hexane, and carbides thereof.

The metal material (excluding lithium-titanium complex oxides) to beused as the negative electrode active material may be any compound thatcan occlude and release lithium, and examples thereof include simplelithium, simple metals and alloys that constitute lithium alloys, andoxides, carbides, nitrides, silicides, sulfides, and phosphides thereof.The simple metals and alloys constituting lithium alloys are preferablymaterials containing any of metal and semi-metal elements in the Groups13 and 14, more preferably simple metal of aluminum, silicon, and tin(hereinafter, referred to as “specific metal elements”), and alloys andcompounds containing any of these atoms. These materials may be usedalone or in combination of two or more at any ratio.

Examples of the negative electrode active material having at least oneatom selected from the specific metal elements include simple metal ofany one specific metal element, alloys of two or more specific metalelements, alloys of one or two or more specific metal elements and oneor two or more other metal elements, compounds containing one or two ormore specific metal elements, and composite compounds such as oxides,carbides, nitrides, silicides, sulfides, and phosphides of thecompounds. Use of such a simple metal, alloy, or metal compound as thenegative electrode active material can give a high capacity tobatteries.

Examples thereof further include compounds in which any of the abovecomposite compounds are complexly bonded with several elements such assimple metals, alloys, and nonmetal elements. Specifically, in the caseof silicon or tin, for example, an alloy of this element and a metalthat does not serve as a negative electrode can be used. In the case oftin, for example, a composite compound including a combination of 5 or 6elements, including tin, a metal (excluding silicon) that serves as anegative electrode, a metal that does not serve as a negative electrode,and a nonmetal element, can be used.

Specific examples thereof include simple Si, SiB₄, SiB₆, Mg₂Si, Ni₂Si,TiSi₂, MoSi₂, CoSi₂, NiSi₂, CaSi₂, CrSi₂, Cu₆Si, FeSi₂, MnSi₂, NbSi₂,TaSi₂, VSi₂, WSi₂, ZnSi₂, SiC, Si₃N₄, Si₂N₂O, SiOv (0<v≤2), LiSiO,simple tin, SnSiO₃, LiSnO, Mg₂Sn, and SnOw (0<w≤2).

Examples thereof further include composite materials of Si or Sn used asa first constitutional element, and second and third constitutionalelements. The second constitutional element is at least one selectedfrom cobalt, iron, magnesium, titanium, vanadium, chromium, manganese,nickel, copper, zinc, gallium, and zirconium, for example. The thirdconstitutional element is at least one selected from boron, carbon,aluminum, and phosphorus, for example.

In order to achieve a high battery capacity and excellent batterycharacteristics, the metal material is preferably simple silicon or tin(which may contain trace impurities), SiOv (0<v≤2), SnOw (0<w≤2), aSi—Co—C composite material, a Si—Ni—C composite material, a Sn—Co—Ccomposite material, or a Sn—Ni—C composite material.

The lithium-containing metal complex oxide material to be used as thenegative electrode active material may be any material that can occludeand release lithium. In order to achieve good high-current-densitycharge and discharge characteristics, materials containing titanium andlithium are preferred, lithium-containing metal complex oxide materialscontaining titanium are more preferred, and complex oxides of lithiumand titanium (hereinafter, abbreviated as “lithium titanium complexoxides”) are still more preferred. In other words, use of aspinel-structured lithium titanium complex oxide contained in thenegative electrode active material for electrolyte batteries isparticularly preferred because such a compound markedly reduces theoutput resistance.

Preferred examples of the lithium titanium complex oxides includecompounds represented by the following formula (O):Li_(x)Ti_(y)M_(z)O₄  (O)wherein M is at least one element selected from the group consisting ofNa, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.

Particularly preferred compositions represented by the formula (O) arethose satisfying one of the following:

(i) 1.2≤x≤1.4, 1.5≤y≤1.7, z=0

(ii) 0.9≤x≤1.1, 1.9≤y≤2.1, z=0

(iii) 0.7≤x≤0.9, 2.1≤y≤2.3, z=0

because the compound structure satisfying any of these compositionsgives good balance of the battery performance.

Particularly preferred representative compositions of the compound areLi_(4/3)Ti_(5/3)O₄ corresponding to the composition (i), Li₁Ti₂O₄corresponding to the composition (ii), and Li_(4/5)Ti_(11/5)O₄corresponding to the composition (iii). Preferred examples of thestructure satisfying Z≠0 include Li_(4/3)Ti_(4/3)Al_(1/3)O₄.

The negative electrode mixture preferably further contains a binder, athickening agent, and a conductive material.

Examples of the binder include the same binders as those mentioned forthe positive electrode. The proportion of the binder relative to thenegative electrode active material is preferably 0.1 mass % or more,more preferably 0.5 mass % or more, particularly preferably 0.6 mass %or more, while preferably 20 mass % or less, more preferably 15 mass %or less, still more preferably 10 mass % or less, particularlypreferably 8 mass % or less. If the proportion of the binder relative tothe negative electrode active material exceeds the above range, a largeamount of the binder may fail to contribute to the battery capacity, sothat the battery capacity may be low. If the proportion is lower thanthe above range, the negative electrode may have a lowered strength.

In particular, in the case of using a rubbery polymer typified by SBR asa main component, the proportion of the binder relative to the negativeelectrode active material is usually 0.1 mass % or more, preferably 0.5mass % or more, more preferably 0.6 mass % or more, while usually 5 mass% or less, preferably 3 mass % or less, more preferably 2 mass % orless. In the case of using a fluoropolymer typified by polyvinylidenefluoride as a main component, the proportion of the binder relative tothe negative electrode active material is usually 1 mass % or more,preferably 2 mass % or more, more preferably 3 mass % or more, whileusually 15 mass % or less, preferably 10 mass % or less, more preferably8 mass % or less.

Examples of the thickening agent include the same thickening agents asthose mentioned for the positive electrode. The proportion of thethickening agent relative to the negative electrode active material isusually 0.1 mass % or more, preferably 0.5 mass % or more, still morepreferably 0.6 mass % or more, while usually 5 mass % or less,preferably 3 mass % or less, still more preferably 2 mass % or less. Ifthe proportion of the thickening agent relative to the negativeelectrode active material is below this range, easiness of applicationmay be significantly impaired. If the proportion thereof exceeds theabove range, the proportion of the negative electrode active material inthe negative electrode active material layer is low, so that thecapacity of the battery may be low or the resistance between thenegative electrode active materials may be high.

Examples of the conductive material of the negative electrode includemetal materials such as copper and nickel; and carbon materials such asgraphite and carbon black.

The solvent for forming slurry may be any solvent that can dissolve ordisperse therein the negative electrode active material and the binder,as well as a thickening agent and a conductive material that are used asnecessary. The slurry-forming solvent may be either an aqueous solventor an organic solvent.

Examples of the aqueous solvent include water and alcohols. Examples ofthe organic solvent include N-methylpyrrolidone (NMP),dimethylformamide, dimethyl acetamide, methyl ethyl ketone,cyclohexanone, methyl acetate, methyl acrylate, diethyl triamine,N,N-dimethyl aminopropyl amine, tetrahydrofuran (THF), toluene, acetone,diethyl ether, dimethyl acetamide, hexamethyl phosphramide, dimethylsulfoxide, benzene, xylene, quinoline, pyridine, methyl naphthalene, andhexane.

Examples of the material of the current collector for negativeelectrodes include copper, nickel, and stainless steel. For easyprocessing of the material into a film and low cost, copper ispreferred.

The current collector usually has a thickness of 1 μm or greater,preferably 5 μm or greater, while usually 100 μm or smaller, preferably50 μm or smaller. Too thick a negative electrode current collector maycause an excessively low capacity of the whole battery, whereas too thina current collector may be difficult to handle.

The negative electrode may be produced by a usual method. One example ofthe production method is a method in which the negative electrodematerial is mixed with the aforementioned binder, thickening agent,conductive material, solvent, and other components to form a slurry-likemixture, and then this mixture is applied to a current collector, dried,and pressed so as to be densified. In the case of using an alloyedmaterial, a thin film layer containing the above negative electrodeactive material (negative electrode active material layer) can beproduced by vapor deposition, sputtering, plating, or a like technique.

The electrode formed from the negative electrode active material mayhave any structure. The density of the negative electrode activematerial existing on the current collector is preferably 1 g·cm⁻³ orhigher, more preferably 1.2 g·cm⁻³ or higher, particularly preferably1.3 g·cm⁻³ or higher, whereas the density thereof is preferably 2.2g·cm⁻³ or lower, more preferably 2.1 g·cm⁻³ or lower, still morepreferably 2.0 g·cm⁻³ or lower, particularly preferably 1.9 g·cm⁻³ orlower. If the density of the negative electrode active material existingon the current collector exceeds the above range, the particles of thenegative electrode active material may be broken, the initialirreversible capacity may be high, and the permeability of theelectrolyte solution toward the vicinity of the interface between thecurrent collector and the negative electrode active material may beimpaired, so that the high-current-density charge and dischargecharacteristics may be impaired. If the density thereof is below theabove range, the conductivity between the negative electrode activematerials may be impaired, the resistance of the battery may be high,and the capacity per unit volume may be low.

The thickness of the negative electrode plate is a design matter inaccordance with the positive electrode plate to be used, and may be anyvalue. The thickness of the mixture layer excluding the thickness of thebase metal foil is usually 15 μm or greater, preferably 20 μm orgreater, more preferably 30 μm or greater, while usually 300 μm orsmaller, preferably 280 μm or smaller, more preferably 250 μm orsmaller.

To the surface of the negative electrode plate may be attached asubstance having a different composition. Examples of the substanceattached to the surface include oxides such as aluminum oxide, siliconoxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide,boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithiumsulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calciumsulfate, and aluminum sulfate; and carbonates such as lithium carbonate,calcium carbonate, and magnesium carbonate.

<Separator>

The lithium ion secondary battery preferably further includes aseparator.

The separator may be formed from any known material and may have anyknown shape as long as the resulting separator is stable to theelectrolyte solution and has excellent liquid-retaining ability. Theseparator is preferably in the form of a porous sheet or a nonwovenfabric which is formed from a material stable to the electrolytesolution, such as resin, glass fiber, or inorganic matter, and which hasexcellent liquid-retaining ability.

Examples of the material of a resin or glass-fiber separator includepolyolefins such as polyethylene and polypropylene, aromatic polyamide,polytetrafluoroethylene, polyether sulfone, and glass filters. Thesematerials may be used alone or in any combination of two or more at anyratio, for example, in the form of a polypropylene/polyethylene bilayerfilm or a polypropylene/polyethylene/polypropylene trilayer film. Inorder to achieve good permeability of the electrolyte solution and agood shut-down effect, the separator is particularly preferably a poroussheet or a nonwoven fabric formed from polyolefin such as polyethyleneor polypropylene.

The separator may have any thickness, and the thickness is usually 1 μmor larger, preferably 5 μm or larger, more preferably 8 μm or larger,while usually 50 μm or smaller, preferably 40 μm or smaller, morepreferably 30 μm or smaller. If the separator is significantly thinnerthan the above range, the insulation and mechanical strength may bepoor. If the separator is significantly thicker than the above range,not only the battery performance, such as rate characteristics, may bepoor but also the energy density of the whole electrolyte battery may below.

If the separator is a porous one such as a porous sheet or a nonwovenfabric, the separator may have any porosity. The porosity is usually 20%or higher, preferably 35% or higher, more preferably 45% or higher,while usually 90% or lower, preferably 85% or lower, more preferably 75%or lower. If the porosity is significantly lower than this range, thefilm resistance tends to be high and the rate characteristics tend to bepoor. If the porosity is significantly higher than this range, themechanical strength of the separator tends to be low and the insulationtends to be poor.

The separator may also have any average pore size. The average pore sizeis usually 0.5 μm or smaller, preferably 0.2 μm or smaller, whereas theaverage pore size is usually 0.05 μm or larger. If the average pore sizeexceeds this range, short circuits may easily occur. If the average poresize is lower than this range, the film resistance may be high and therate characteristics may be poor.

Examples of the inorganic material include oxides such as alumina andsilicon dioxide, nitrides such as aluminum nitride and silicon nitride,and sulfates such as barium sulfate and calcium sulfate, each of whichis in the form of particles or fibers.

The separator is in the form of a thin film such as a nonwoven fabric, awoven fabric, or a microporous film. The thin film favorably has a poresize of 0.01 to 1 μm and a thickness of 5 to 50 μm. In addition to theform of the above separate thin film, the separator may have a structurein which a composite porous layer containing particles of the aboveinorganic material is formed on the surface of one or both of thepositive and negative electrodes using a resin binder. For example,alumina particles having a 90% particle size of smaller than 1 μm areapplied to the respective surfaces of the positive electrode withfluororesin used as a binder to form a porous layer.

<Battery Design>

The electrode group may be either a laminated structure including theabove positive and negative electrode plates with the above separator inbetween, or a wound structure including the above positive and negativeelectrode plates in spiral with the above separator in between. Theproportion of the volume of the electrode group in the battery internalvolume (hereinafter, referred to as an electrode group proportion) isusually 40% or higher, preferably 50% or higher, while usually 90% orlower, preferably 80% or lower.

If the electrode group proportion is lower than the above range, thebattery capacity may be low. If the electrode group proportion exceedsthe above range, the battery may have small space for voids. Thus, whenthe battery temperature rises to high temperature, the components mayexpand or the liquid fraction of the electrolyte solution shows a highvapor pressure, so that the internal pressure rises. As a result, thebattery characteristics such as charge and discharge repeatability andthe high-temperature storageability may be impaired, and a gas-releasingvalve for releasing the internal pressure toward the outside may work.

The current-collecting structure may be any structure. In order to moreeffectively improve the high-current-density charge and dischargecharacteristics by the electrolyte solution, the current-collectingstructure is preferably a structure which reduces the resistances atwiring portions and jointing portions. When the internal resistance isreduced in such a manner, the effects of using the electrolyte solutioncan particularly favorably be achieved.

In an electrode group having the above layered structure, the metal coreportions of the respective electrode layers are preferably bundled andwelded to a terminal. If one electrode has a large area, the internalresistance is high. Thus, multiple terminals may preferably be formed inthe electrode to reduce the resistance. In an electrode group having thewound structure, multiple lead structures may be disposed on each of thepositive electrode and the negative electrode and bundled to a terminal.Thereby, the internal resistance can be reduced.

The external case may be made of any material that is stable to anelectrolyte solution to be used. Specific examples thereof includemetals such as nickel-plated steel plates, stainless steel, aluminum andaluminum alloys, and magnesium alloys, and layered film (laminate film)of resin and aluminum foil. In order to reduce the weight, a metal suchas aluminum or an aluminum alloy or a laminate film is favorably used.

External cases made of metal may have a sealed-up structure formed bywelding the metal by laser welding, resistance welding, or ultrasonicwelding or a caulking structure using the metal via a resin gasket.External cases made of a laminate film may have a sealed-up structureformed by hot-melting the resin layers. In order to improve thesealability, a resin which is different from the resin of the laminatefilm may be disposed between the resin layers. Especially, in the caseof forming a sealed-up structure by hot-melting the resin layers viacurrent-collecting terminals, metal and resin are to be bonded. Thus,the resin to be disposed between the resin layers is favorably a resinhaving a polar group or a modified resin having a polar group introducedthereinto.

The lithium ion secondary battery may have any shape, and examplesthereof include cylindrical batteries, square batteries, laminatedbatteries, coin batteries, and large-size batteries. The shapes and theconfigurations of the positive electrode, the negative electrode, andthe separator may be changed in accordance with the shape of thebattery.

The electrochemical device or secondary battery that includes the aboveelectrolyte solution can be suitably used for a module. This modulepreferably includes an electrochemical device or secondary batteryincluding the above electrolyte solution.

Examples of the electrochemical device using the electrolyte solutioninclude an electric double-layer capacitor.

In the electric double-layer capacitor, one or both of the positiveelectrode and the negative electrode is/are a polarizable electrode. Thepolarizable electrode and a non-polarizable electrode may be thefollowing electrodes specifically disclosed in JP H09-7896 A.

The polarizable electrode mainly containing activated carbon ispreferably one containing inactive carbon having a large specificsurface area and a conducting agent (e.g., carbon black) which impartselectronic conductivity. The polarizable electrode can be formed byvarious methods. For example, a polarizable electrode containingactivated carbon and carbon black can be formed by mixing activatedcarbon powder, carbon black, and a phenolic resin, press-molding themixture, and then firing and activating the mixture in an inert gasatmosphere and in a steam atmosphere. This polarizable electrode ispreferably bonded to a current collector using, for example, aconductive adhesive.

Alternatively, a polarizable electrode may be formed by kneadingactivated carbon powder, carbon black, and a binder in the presence ofan alcohol to form a sheet-like mixture, and then drying the sheet-likemixture. This binder may be polytetrafluoroethylene, for example.Alternatively, a polarizable electrode integrated with a currentcollector may be formed by mixing activated carbon powder, carbon black,a binder, and a solvent to form slurry, applying this slurry to a metalfoil of a current collector, and drying the applied slurry.

Both electrodes of the electric double-layer capacitor may bepolarizable electrodes mainly containing activated carbon.Alternatively, the electric double-layer capacitor may have a structurein which one electrode thereof is a non-polarizable electrode. Examplesof such a structure include a combination of a positive electrode mainlycontaining a cell active material such as a metal oxide and a negativeelectrode which is a polarizable electrode mainly containing activatedcarbon; and a combination of a negative electrode mainly containing acarbon material that can reversibly occlude and release lithium ions ora negative electrode of metallic lithium or a lithium alloy and apolarizable electrode mainly containing activated carbon.

In place of or in combination with activated carbon, a carbonaceousmaterial may be used such as carbon black, graphite, expanded graphite,porous carbon, carbon nanotube, carbon nanohorn, and ketjen black.

The non-polarizable electrode is preferably an electrode mainlycontaining a carbon material that can reversibly occlude and releaselithium ions, and this carbon material is made to occlude lithium ionsin advance. In this case, the electrolyte used is a lithium salt. Theelectric double-layer capacitor having such a configuration achieves amuch higher withstand voltage of exceeding 4 V.

The solvent to be used for preparation of slurry in the production of anelectrode is preferably one that dissolves a binder. The solvent isappropriately selected from N-methylpyrrolidone, dimethylformamide,toluene, xylene, isophorone, methyl ethyl ketone, ethyl acetate, methylacetate, dimethyl phthalate, ethanol, methanol, butanol, and water inaccordance with the type of the binder.

Examples of the activated carbon to be used for a polarizable electrodeinclude phenol resin-based activated carbon, coconut shell-basedactivated carbon, and petroleum coke-based activated carbon. In order toachieve a large capacity, petroleum coke-based activated carbon orphenol resin-based activated carbon is preferred. Further, examples ofan activation method to prepare activated carbon include steamactivation and molten KOH activation. In order to achieve a largercapacity, the use of activated carbon obtainable by the molten KOHactivation is preferred.

Preferred examples of the conducting agent to be used for a polarizableelectrode include carbon black, ketjen black, acetylene black, naturalgraphite, artificial graphite, metal fibers, conductive titanium oxide,and ruthenium oxide. In order to achieve good conductivity (low internalresistance), and since too large an amount of the conducting agent maylower the capacity of a product, the amount of the conducting agent(e.g., carbon black) to be used for a polarizable electrode ispreferably 1 to 50 mass % in the sum of the amounts of the conductingagent and the activated carbon.

In order to provide an electric double-layer capacitor having a largecapacity and a low internal resistance, the activated carbon to be usedfor a polarizable electrode is preferably activated carbon having anaverage particle size of 20 μm or smaller and a specific surface area of1500 to 3000 m²/g. Preferred examples of the carbon material forproviding an electrode mainly containing a carbon material that canreversibly occlude and release lithium ions include natural graphite,artificial graphite, graphitized mesocarbon microsphere, graphitizedwhisker, vapor-grown carbon fiber, sintered furfuryl alcohol resin, andsintered novolak resin.

The current collector may be any one which is chemically andelectrochemically resistant to corrosion. Preferred examples of thecurrent collector of a polarizable electrode mainly containing activatedcarbon include stainless steel, aluminum, titanium, and tantalum.Stainless steel or aluminum is a particularly preferred material amongthese in terms of both the characteristics and cost of the resultingelectric double-layer capacitor. Preferred examples of the currentcollector to be used for the electrode mainly containing a carbonmaterial that can reversibly occlude and release lithium ions includestainless steel, copper, and nickel.

Examples of methods of allowing the carbon material that can reversiblyocclude and release lithium ions to occlude lithium ions in advanceinclude (1) a method of mixing powdery lithium in advance to a carbonmaterial that can reversibly occlude and release lithium ions, (2) amethod of placing lithium foil on an electrode including a carbonmaterial that can reversibly occlude and release lithium ions and abinder so that the lithium foil is electrically in contact with theelectrode, immersing this electrode in an electrolyte solutioncontaining a lithium salt dissolved therein so that the lithium isionized, and allowing the carbon material to take in the resultinglithium ions, and (3) a method of placing an electrode including acarbon material that can reversibly occlude and release lithium ions anda binder at a minus side and placing a lithium metal at a plus side,immersing the electrodes in a non-aqueous electrolyte solutioncontaining a lithium salt as an electrolyte, and supplying a current sothat the carbon material is allowed to electrochemically take in theionized lithium.

Examples of commonly known electric double-layer capacitors includewound-type electric double-layer capacitors, laminate-type electricdouble-layer capacitors, and coin-type electric double-layer capacitors.The electric double-layer capacitor may be of any of these types.

For example, a wound-type electric double-layer capacitor may beassembled by winding a positive electrode and a negative electrode eachhaving a laminate (electrode) of a current collector and an electrodelayer with a separator in between to form a wound element, putting thiswound element into a case made of, for example, aluminum, filling thecase with an electrolyte solution, preferably a non-aqueous electrolytesolution, and then sealing the case with a rubber sealing material.

In the present invention, the separator may be formed from anyconventionally known material and may have a conventionally knownstructure. Examples thereof include a polyethylene porous membrane, andnonwoven fabric of polypropylene fibers, glass fibers, or cellulosefibers.

Alternatively, by a known method, an electric double-layer capacitor maybe prepared in the form of a laminate-type electric double layercapacitor including a sheet-like positive and negative electrodesstacked with each other with an electrolyte solution and a separator inbetween, or in the form of a coin-type electric double-layer capacitorincluding a positive electrode and a negative electrode fixed in a coinshape using a gasket with an electrolyte solution and a separator inbetween.

As mentioned above, use of the electrolyte solution can suitably providesecondary batteries having excellent storage capacity retention, modulesusing the secondary batteries, and electric double-layer capacitors.

EXAMPLES

The present invention will be described with reference to, but notlimited to, examples.

Synthesis Example 1

Bromovinylene carbonate represented by the following formula wassynthesized according to the method disclosed in Chem. Ber. 103, 1970,3949.

A 500-mL glass reactor was charged with 7.93 g of zinc, 3.50 g oftetrakistriphenylphosphinepalladium, 10.00 g of bromovinylene carbonate,and 150.00 ml of cyclopentyl methyl ether. Then, 52.43 g ofperfluorobutyl iodide was dropwise added under ultrasonic irradiation,and the components were stirred for 6 hours at room temperature.

After the reaction aged, 150.00 g of a saturated aqueous solution ofsodium chloride was added so that the reaction was quenched. Thereaction solution was extracted with diisopropyl ether, and thenmagnesium sulfate was added so that the extract was dried. Then, thedried product was concentrated and purified by sublimation. Thereby,1.16 g of 4-perfluorobutyl-vinylene carbonate (C₄F₉VC), the targetcompound, was obtained as a white solid.

The analysis showed that 4-perfluorobutyl-vinylene carbonate representedby the following formula was obtained.

¹H-NMR (acetone-d6): δ8.45 (t, J=2.39 Hz, 1H)

¹³C-NMR (acetone-d6): δ110.13 to 111.05 (m), 112.49 to 114.03 (m),116.52 (t, J=133.90 Hz), 119.38 (t, J=133.90 Hz), 132.18 (t, J=139.89Hz), 136.02 (t, J=23.98 Hz), 151.23

¹⁹F-NMR (acetone-d6): δ−79.43 (t, J=10.53 Hz, 3F), −113.39 (t, J=12.03Hz, 2F), −121.56 (dd, J=8.56, 2.26 Hz, 2F), −124.18 to −124.26 (m, 2F)

Synthesis Example 2

Bromovinylene carbonate represented by the following formula wassynthesized according to the method disclosed in Chem. Ber. 103, 1970,3949.

A 500-mL glass reactor was charged with 15.44 g of copper, 50.85 g of(C₆F₁₃)₂Hg, and 90.00 ml of dimethylacetamide, and the components werestirred for 2 hours at 140° C. Then, 10.00 g of bromovinylene carbonatedissolved in 90.00 ml of dimethylacetamide was dropwise added and thecomponents were stirred for 6 hours at 140° C.

After the reaction aged, 100.00 g of a saturated aqueous solution ofsodium chloride was added so that the reaction was quenched. Thereaction solution was extracted with ethyl acetate, and then magnesiumsulfate was added so that the extract was dried. Then, the dried productwas concentrated and purified by sublimation. Thereby, 4.73 g of4-perfluorohexyl-vinylene carbonate (C₆F₁₃VC), the target compound, wasobtained as a white solid.

The analysis showed that 4-perfluorohexyl-vinylene carbonate representedby the following formula was obtained.

¹H-NMR (acetone-d6): δ8.47 (t, J=2.39 Hz, 1H)

¹³C-NMR (acetone-d6): δ105.97 to 107.27 (m), 108.52 to 109.83 (m),111.06 to 112.20 (m), 114.32 (t, J=130.69 Hz), 117.18 (t, J=130.69 Hz),120.05 (t, J=137.09 Hz), 129.91 (t, J=136.69 Hz), 134.29 (t, J=25.18Hz), 149.24

¹⁹F-NMR (acetone-d6): δ−81.71 (t, J=9.02 Hz, 3F), −115.71 (t, J=12.03Hz, 2F), −122.47 (s, 2F), −123.17 (d, J=6.76 Hz, 2F), −123.42 (d, J=7.14Hz, 2F), −126.76 to −126.85 (m, 2F)

Synthesis Example 3

Bromovinylene carbonate represented by the following formula wassynthesized according to the method disclosed in Chem. Ber. 103, 1970,3949.

A 500-mL glass reactor was charged with 1.15 g of copper iodide, 200.00ml of dimethylpropyleneurea, 7.04 g of potassium fluoride, 35.43 g ofC₄F₉TMS, and 1.09 g of 1,10-phenanthroline. Then, 10.00 g ofbromovinylene carbonate was dropwise added, and the components werestirred for 20 hours at 80° C.

After the reaction aged, 100.00 g of a saturated aqueous solution ofsodium chloride was added so that the reaction was quenched. Thereaction solution was extracted with ethyl acetate, and then magnesiumsulfate was added so that the extract was dried. Then, the dried productwas concentrated and purified by sublimation. Thereby, 9.07 g of4-perfluorobutyl-vinylene carbonate (C₄F₉VC), the target compound, wasobtained as a white solid.

The analysis showed that 4-perfluorobutyl-vinylene carbonate representedby the following formula was obtained.

Synthesis Example 4

A 1000-mL photo-reactor was equipped with a 100-W high-pressure mercurylamp, and charged with 20.00 g of 4-perfluorohexyl-ethylene carbonaterepresented by the following formula and 197.00 mL of carbontetrachloride.

Under light irradiation from the high-pressure mercury lamp, 9.44 g ofbromine dissolved in 98.49 mL of carbon tetrachloride was dropwiseadded. This dropwise addition was followed by stirring for 2 hours atroom temperature. After the reaction aged, 186.22 g of a 10% aqueoussolution of sodium sulfite was added so that the reaction was quenched.Then, an organic layer obtained by liquid separation was used in thenext step as a reaction solution. The reaction solution contains acarbonate represented by the following formula.

The reaction solution obtained in the above procedure was put into a1000-mL glass reactor, and 5.98 g of triethylamine was dropwise addedunder ice cooling. This dropwise addition was followed by stirring for 3hours. After the reaction aged, 113.54 g of a 10% aqueous solution ofcitric acid was added so that the reaction was quenched. Then, magnesiumsulfate was added to an organic layer obtained by liquid separation sothat the organic layer was dried. The magnesium sulfate was filtered outand the filtrate was concentrated. Thereby, crude4-perfluorohexyl-carbonate was obtained.

The crude product was then purified by sublimation. Thereby, 4.36 g of4-perfluorohexyl-vinylene carbonate (C₆F₁₃VC), the target compound, wasobtained as a white solid.

The analysis showed that 4-perfluorohexyl-vinylene carbonate representedby the following formula was obtained.

Synthesis Example 5

A 1000-mL photo-reactor was equipped with a 100-W high-pressure mercurylamp, and charged with 20.00 g of 4-perfluorobutyl-ethylene carbonaterepresented by the following formula and 261.37 mL of carbontetrachloride.

Under light irradiation from the high-pressure mercury lamp, 12.53 g ofbromine dissolved in 130.68 mL of carbon tetrachloride was dropwiseadded. This dropwise addition was followed by stirring for 2 hours atroom temperature. After the reaction aged, 247.07 g of a 10% aqueoussolution of sodium sulfite was added so that the reaction was quenched.Then, an organic layer obtained by liquid separation was used in thenext step as a reaction solution. The reaction solution contains acarbonate represented by the following formula.

The reaction solution obtained in the above procedure was put into a1000-mL glass reactor, and 7.93 g of triethylamine was dropwise addedunder ice cooling. This dropwise addition was followed by stirring for 3hours. After the reaction aged, 150.64 g of a 10% aqueous solution ofcitric acid was added so that the reaction was quenched. Then, magnesiumsulfate was added to an organic layer obtained by liquid separation sothat the organic layer was dried. The magnesium sulfate was filtered outand the filtrate was concentrated. Thereby, crude4-perfluorobutyl-vinylene carbonate was obtained.

The crude product was then purified by sublimation. Thereby, 5.05 g of4-perfluorobutyl-vinylene carbonate, the target compound, was obtainedas a white solid.

The analysis showed that 4-perfluorobutyl-vinylene carbonate representedby the following formula was obtained.

Synthesis Example 6

A 200-mL glass reactor was equipped with a condenser, and charged with2.15 g of LiBr and 40.00 mL of N-methylpyrrolidone (NMP). Then, thecomponents were stirred for 1 hour at 35° C. The atmosphere inside thereactor was replaced by carbon dioxide, and 10.00 g of an epoxyrepresented by the following formula was dropwise added. This dropwiseaddition was followed by stirring for 6 hours at 35° C.

After the reaction aged, 20 mL of a saturated aqueous solution of sodiumchloride was added so that the reaction was quenched. The reactionsolution was extracted with ethyl acetate, and then magnesium sulfatewas added so that the extract was dried. Then, the dried product wasconcentrated. Thereby, a carbonate represented by the following formulawas obtained.

The carbonate obtained in the above procedure and 53.60 mL of diethylether were put into a 300-mL glass reactor, and 6.51 g of triethylaminewas dropwise added under ice cooling. This dropwise addition wasfollowed by stirring for 3 hours. After the reaction aged, 123.58 g of a10% aqueous solution of citric acid was added so that the reaction wasquenched. Then, magnesium sulfate was added to an organic layer obtainedby liquid separation so that the organic layer was dried. The magnesiumsulfate was filtered out and the filtrate was concentrated. Thereby,crude 4-trifluoromethyl-vinylene carbonate was obtained.

The crude product was then purified by distillation. Thereby, 3.77 g of4-trifluoromethyl-vinylene carbonate (CF₃VC), the target compound, wasobtained as a colorless liquid.

The analysis showed that 4-trifluoromethyl-vinylene carbonaterepresented by the following formula was obtained.

Synthesis Example 7

A 300-mL autoclave was charged with 10.00 g of vinylene carbonate,103.65 g of perfluorohexyl iodide, and 1.02 g oft-butylperoxyisopropylmonocarbonate, and the components were stirred for6 hours at 120° C. After the reaction aged, the reaction solution wasconcentrated. Thereby, crude C₆F₁₃ECI was obtained as a white solid.C₆F₁₃ECI is a carbonate represented by the following formula.

Next, 61.45 g of the crude C₆F₁₃ECI and 231.02 mL of diethyl ether wereput into a 500-mL glass reactor. Then, 14.03 g of triethylamine wasdropwise added under ice cooling. This dropwise addition was followed bystirring for 3 hours. After the reaction aged, 159.78 g of a 20% aqueoussolution of citric acid was added so that the reaction was quenched. Thereaction solution was extracted with diethyl ether, and then magnesiumsulfate was added so that the extract was dried. Then, the dried productwas concentrated and purified by sublimation. Thereby, 31.02 g of4-perfluorohexyl-vinylene carbonate (C₆F₁₃VC), the target compound, wasobtained as a white solid.

The analysis showed that 4-perfluorohexyl-vinylene carbonate representedby the following formula was obtained.

Synthesis Example 8

A 300-mL autoclave was charged with 10.00 g of vinylene carbonate, 80.40g of perfluorobutyl iodide, and 1.02 g oft-butylperoxyisopropylmonocarbonate, and the components were stirred for6 hours at 120° C. After the reaction aged, the reaction solution wasconcentrated. Thereby, crude C₄F₉ECI was obtained as a white solid.C₄F₉ECI is a carbonate represented by the following formula.

Next, 49.50 g of the crude C₄F₉ECI and 229.18 mL of diethyl ether wereput into a 500-mL glass reactor. Then, 13.91 g of triethylamine wasdropwise added under ice cooling. This dropwise addition was followed bystirring for 3 hours. After the reaction aged, 158.51 g of a 20% aqueoussolution of citric acid was added so that the reaction was quenched. Thereaction solution was extracted with diethyl ether, and then magnesiumsulfate was added so that the extract was dried. Then, the dried productwas concentrated and purified by sublimation. Thereby, 24.42 g of4-perfluorobutyl-vinylene carbonate (C₄F₉VC), the target compound, wasobtained as a white solid.

The analysis showed that 4-perfluorobutyl-vinylene carbonate representedby the following formula was obtained.

Experiment 1 (Evaluation of 4.2-V Lithium Battery) Example 1

In dry argon atmosphere, 0.5 parts by weight of4-perfluorohexyl-vinylene carbonate obtained in Synthesis Example 4 and0.5 parts by weight of vinylene carbonate (VC) were added to 99 parts byweight of a mixture of ethylene carbonate and ethyl methyl carbonate(volume ratio=3:7). Then, sufficiently dried LiPF₆ was dissolved thereinso as to have a concentration of 1 mol/L. Thereby, an electrolytesolution was prepared.

(Production of Laminate Battery)

LiNi_(1/3)Mn_(1/3)Co_(1/3)O₂, carbon black, and polyvinylidene fluoride(trade name: KF-7200, Kureha Chemical Industry Co., Ltd.) were mixed ata ratio of 92/3/5 (mass % ratio) to provide a positive electrode activematerial. This positive electrode active material was dispersed inN-methyl-2-pyrrolidone to form a positive electrode mixture slurry. Theresulting positive electrode mixture slurry was uniformly applied ontoan aluminum current collector and dried to provide a positive electrodemixture layer (thickness: 50 μm). Then, the workpiece wascompression-molded using a roller press. Thereby, a positive electrodelaminate was produced.

Separately, styrene-butadiene rubber dispersed in distilled water wasadded to artificial graphite powder such that the solid content of therubber was 6 mass %, and the components were mixed using a disperser toform a slurry-like mixture. This mixture was uniformly applied onto anegative electrode current collector (10-μm-thick copper foil) anddried. Thereby, a negative electrode mixture layer was formed. Then, theworkpiece was compression-molded using a roller press. Thereby, anegative electrode laminate was produced.

The positive electrode laminate and the negative electrode laminate wereoppositely disposed with a 20-μm-thick microporous polyethylene film(separator) interposed in between, and wound to provide a wound article.This wound article was placed in an aluminum-laminated film and anelectrolyte solution was put thereinto. After the electrolyte solutionsufficiently permeated into the separator and other desired components,the package was sealed, pre-charged, and aged. Thereby, a 1-Ah lithiumion secondary battery was produced.

(Measurement of Battery Performance)

For a coin-type lithium secondary battery, the cycle characteristics andthe high-temperature storage characteristics at high voltage wereanalyzed as follows.

Charge and Discharge Conditions

Charge: 1 C, 4.2 V, retained until the charge current reaches 1/10 C(CC/CV charge)

Discharge: 1 C, 3.0 V cut (CC discharge)

(High-Temperature Storage Characteristics)

For the high-temperature storage characteristics, the battery wascharged and discharged according to the above charge and dischargeconditions (charged at 1.0 C and a predetermined voltage until thecharge current reached 1/10 C, and discharged at a current correspondingto 1 C until the voltage reached 3.0 V), whereby the discharge capacitywas examined. Then, the battery was again charged according to the abovecharge conditions, and then stored in a 85° C. temperature-constantchamber for 3 days. The battery after the storage was placed in a 25° C.atmosphere, and was discharged according to the above dischargeconditions until the end-of-discharge voltage, 3 V, and the residualcapacity was measured. The battery was further charged according to theabove charge conditions and discharged according to the above dischargeconditions at a constant current until the end-of-discharge voltage, 3V, and the capacity recovery was measured. Table 1 shows the capacityrecovery relative to the discharge capacity before storage which isdefined as 100.

Table 1 also shows the amount (mL) of gas generated in this case.

Example 2

A battery was produced and the experiment was performed in the samemanner as in Example 1 except that 4-perfluorohexyl-vinylene carbonateprepared in Synthesis Example 4 was replaced by4-perfluorobutyl-vinylene carbonate prepared in Synthesis Example 5.Table 1 shows the results.

Example 3

A battery was produced and the experiment was performed in the samemanner as in Example 1 except that 4-perfluorohexyl-vinylene carbonateprepared in Synthesis Example 4 was replaced by4-trifluoromethyl-vinylene carbonate prepared in Synthesis Example 6.Table 1 shows the results.

Comparative Example 1

A battery was produced and the experiment was performed in the samemanner as in Example 1 except that the amount of VC was increased by 0.5wt % (i.e., 1.0 part by weight of VC was added in total) instead ofadding 4-perfluorohexyl-vinylene carbonate. Table 1 shows the results.

TABLE 1 High-temperature storage characteristics Capacity recoveryAmount of gas Example 1 92.1 0.73 Example 2 93.2 0.60 Example 3 93.90.55 Comparative Example 1 85.2 0.97

Comparison between Examples 1 to 3 and Comparative Example 1 in Table 1shows that the presence of the compound (1) led to less generation ofgas and higher capacity recovery than the use of VC alone.

What is claimed is:
 1. An electrolyte solution comprising a compoundrepresented by the following formula (1):

wherein Rf is a C1-C8 fluorinated alkyl group, and vinylene carbonate.2. An electrochemical device comprising the electrolyte solutionaccording to claim
 1. 3. A lithium ion secondary battery comprising theelectrolyte solution according to claim
 1. 4. A module comprising thelithium ion secondary battery according to claim 3.